Ionic gel electrolyte, energy storage devices, and methods of manufacture thereof

ABSTRACT

An electrochemical cell includes solid-state, printable anode layer, cathode layer and non-aqueous gel electrolyte layer coupled to the anode layer and cathode layer. The electrolyte layer provides physical separation between the anode layer and the cathode layer, and comprises a composition configured to provide ionic communication between the anode layer and cathode layer by facilitating transmission of multivalent ions between the anode layer and the cathode layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/162,268 filed on May 23, 2016, incorporated herein by reference inits entirety, which is a continuation of U.S. patent application Ser.No. 13/968,603 filed on Aug. 16, 2013, now U.S. Pat. No. 9,368,283,incorporated herein by reference in its entirety, which is acontinuation of U.S. patent application Ser. No. 13/784,935 filed onMar. 5, 2013, now U.S. Pat. No. 9,076,589, incorporated herein byreference in its entirety, which is a 35 U.S.C. § 111(a) continuation ofPCT international application number PCT/US2011/051469 filed on Sep. 13,2011, incorporated herein by reference in its entirety, which claimspriority to and the benefit of U.S. provisional patent application Ser.No. 61/382,027 filed on Sep. 13, 2010, incorporated herein by referencein its entirety. Priority is claimed to each of the foregoingapplications.

The above-referenced PCT international application was published as PCTInternational Publication No. WO 2012/037171 on Mar. 22, 2012 andrepublished on Aug. 2, 2012, and said publications are incorporatedherein by reference in their entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

INCORPORATION-BY-REFERENCE OF COMPUTER PROGRAM APPENDIX

Not Applicable

NOTICE OF MATERIAL SUBJECT TO COPYRIGHT PROTECTION

A portion of the material in this patent document is subject tocopyright protection under the copyright laws of the United States andof other countries. The owner of the copyright rights has no objectionto the facsimile reproduction by anyone of the patent document or thepatent disclosure, as it appears in the United States Patent andTrademark Office publicly available file or records, but otherwisereserves all copyright rights whatsoever. The copyright owner does nothereby waive any of its rights to have this patent document maintainedin secrecy, including without limitation its rights pursuant to 37C.F.R. § 1.14.

BACKGROUND OF THE INVENTION 1. Field of the Invention

This invention relates generally to electrochemical cells, and, morespecifically, to ionic liquid gel electrolyte chemistries and methods ofmaking batteries that can be used with devices as single-use orrechargeable power sources.

2. Description of Related Art

The reduction of electronic device form factors and their power demandshave made it possible to realize new devices that are thin, compact, andlightweight. The evolution of portable devices can be in part attributedto the combination of the advancements in battery electrode materialsand their compatibility with electrolyte materials. For example, thedevelopment of more effective high energy density lithium andlithium-ion electrode materials has enabled portable, compact, highcapacity batteries, while the introduction of lithium and lithium-ionsolid polymer and gel electrolytes has relaxed the battery's requirementfor rigid and hard packaging, spurring the wide-spread adoption ofthinner batteries, hermetically sealed within pouch material. Inaddition to performance and form factor benefits, the use ofsolid-state, polymer, and gel electrolytes have introduced additionalimprovements in battery manufacturability, cost, and inherent safety.Thus, considerable efforts have been dedicated to solid-state, polymer,and gel electrolyte development.

The demand for thin, miniature, and low cost batteries has beenpropelled by the increased ubiquity of low power sensors, wirelessdevices, and printed electronics. The reduction of electronic deviceform factors and their power demands have made it possible to realize afully-integrated microdevice platform, with computation, communication,and sensing capabilities all enabled by an integrated power source. Inparticular, MEMS-based sensors and actuators, especially in autonomous,integrated platforms known as “smart dust” have been huge drivers in thedevelopment of thin format battery and microbattery technology. Theimplications of the widespread deployment of these devices, especiallyautonomous wireless sensor nodes, is pivotal to a variety of fieldsincluding the “internet of things”, wearable electronics to enable the“quantified self”, smart labels, intelligent toys, structuralmonitoring, and cost- and energy-effective regulation of home, industry,and office energy use applications, to name a few. These broad classesof devices require power sources that can supply power in the range ofmicrowatts (μW) to hundreds of milliwatts (mW), and capacities frommicroamp-hours (μAh) to hundreds of milliamp-hours (mAh), depending onthe application. In addition, for many of the portable or ubiquitousapplications, it is desired that the power source is no greater in sizethan the device it powers, and thin in form factor. Finally, low costand mass-manufacturable solutions are critical.

Of the existing battery systems that are being considered for theseapplications, thin film, lithium polymer, and semi-printed batteries arethe forerunners, though each have significant shortcomings that havelimited their widespread adoption. Vapor deposited thin film lithium andlithium-ion batteries have low storage capacities and power capabilitiesdue to materials deposition limitations. Lithium polymer batteries haveleveraged the rapid advancements of pouch cell battery manufacturing,but like thin film lithium and lithium-ion batteries, are plagued bystringent hermetic encapsulation requirements due to its sensitivity tocontamination from the environment. Semi-printed batteries often utilizea liquid electrolyte, adding cell geometry and manufacturingcomplexities.

Such microdevices need power sources with footprints less than 1 cm² andthicknesses on the order of a few mm or less, that can supply power inthe range of microwatts (μW) to milliwatts (mW), depending on theapplication. The need for a micropower source that can satisfy the powerrequirements of such wireless devices and with comparable dimensions hasincited a surge of research within the fields of microfabrication,energy harvesting, and energy storage. For autonomous wireless sensors,the microenergy storage devices currently being considered aremicrobatteries and microcapacitors.

Although microbattery chemistries may be similar to macrobatterychemistries, macrobattery configurations, packaging, and post-processingare not feasible below the centimeter scale. As a result, in addition tomaterials optimization, microbattery researchers have focused heavily onintegrating microbatteries directly onto the same substrates as thedevices they are powering.

An ideal microbattery (or microcapacitor) solution has not yet beenfound. Nickel-zinc systems have the problem that zinc dendrites grow,and the shape of the electrode changes during cycling, thus reducingcycle life. Rechargeable alkaline manganese cells and zinc-silver oxidecells have the same problem. Lithium-ion and lithium polymer systemsrequire strict charge and discharge regulation and pose flammabilityrisks.

What is needed is a safe, long-lasting, inexpensive micropower sourcethat can enable microdevices to be used in a wide variety ofapplications.

BRIEF SUMMARY OF THE INVENTION

In one aspect of the present invention, a polymer is swelled with a roomtemperature ionic liquid electrolyte to form a non-aqueous gel toreplace the traditional alkaline and acidic liquid electrolyte (andseparator) of a zinc-metal oxide battery.

In another aspect of the invention, a printed battery is fabricated froman ionic liquid gel electrolyte sandwiched between a zinc electrode anda metal oxide electrode.

In a further aspect of the invention, an electrochemical cell, comprisesan anode layer; a cathode layer; and a non-aqueous gel electrolyte layercoupled to the anode layer and cathode layer; wherein the electrolytelayer provides physical separation between the anode layer and thecathode layer and comprises a polymer into which at least one ionicliquid and an electrolyte salt have been imbibe. The electrolyte layercomprising a composition configured to provide ionic communicationbetween the anode layer and cathode layer by facilitating transmissionof multivalent ions between the anode layer and the cathode layer.

Another aspect is an electrolyte configured to provide physicalseparation between an anode and the cathode of an electromechanicalcell. The electrolyte includes a room temperature ionic liquidelectrolyte imbibed into a polymer to form a non-aqueous gel, whereinthe electrolyte is configured to provide ionic communication between theanode and cathode by facilitating transmission of multivalent ionsacross the electrolyte.

A further aspect is method of fabricating an electrochemical cellcomprising the steps of: providing a first electrode ink and a secondelectrode ink; providing liquid electrolyte ink; printing a firstelectrode layer of the first electrode ink; printing a layer ofelectrolyte ink; and printing a second electrode layer of secondelectrode ink. The layer of electrolyte ink provides physical separationbetween the first electrode layer and second electrode layer to form anelectrochemical cell, and is configured to provide ionic communicationbetween the first electrode layer and second layer by facilitatingtransmission of multivalent ions between the first electrode layer andthe second electrode layer.

Further aspects of the invention will be brought out in the followingportions of the specification, wherein the detailed description is forthe purpose of fully disclosing preferred embodiments of the inventionwithout placing limitations thereon.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

The invention will be more fully understood by reference to thefollowing drawings which are for illustrative purposes only:

FIG. 1 is a schematic diagram of a printed power source in accordancewith the present invention.

FIG. 2 shows a schematic diagram of alternative 2-D planar cellconfiguration in accordance with the present invention.

FIG. 3 is a schematic diagram of a device incorporating an array ofcells in accordance with the present invention.

FIG. 4 is schematic diagram of a method for of ink synthesis fordispenser printing in accordance with the present invention.

FIGS. 5A through 5D show schematic diagrams for a method of generating aprinted battery in accordance with the present invention.

FIG. 6 is a schematic diagram of a dispenser printer configured forgenerating a printed microbattery in accordance with the presentinvention.

FIG. 7 shows viscosity with respect to applied shear rate for compositeslurry and polymer solution inks. The ranges of shear rates andcorresponding printed feature sizes applied by the dispenser printer arebracketed for both inks.

FIGS. 8A and 8B show micrographs of the ionic liquid/polymer in the gelelectrolyte of the present invention.

FIG. 9 illustrates the electrochemical potential stability of ionicliquid electrolytes with 0 to 0.75 M zinc salt concentrations. Theoccurrence of a large magnitude current density corresponds toelectrolyte decomposition.

FIG. 10 shows the ionic conductivity and viscosity of an ionic liquidelectrolyte as a function of zinc salt concentration.

FIG. 11 illustrates the comparison of ionic conductivities of zinc andlithium ion—ionic liquid electrolyte systems with respect to ionicconcentration.

FIG. 12 shows comparison of diffusion coefficients of the active ions inzinc and lithium ion—ionic liquid electrolyte systems.

FIG. 13 is a plot of voltammagrams of ionic liquid electrolytes withzinc salt concentrations ranging from 0 to 0.75 M.

FIG. 14 illustrates cyclic behavior of the peak zinc dissolution currentdensities measured from ionic liquid electrolytes with zinc saltconcentrations of 0 to 0.75 M.

FIG. 15 shows room temperature ionic conductivities of gels with varyingionic liquid concentrations in PVDF-HFP.

FIG. 16 is a micrograph of the cross section of a zinc, gel electrolyte,and manganese dioxide printed microbattery. The nickel foil currentcollector was removed so that the printed structure could be imaged.

FIG. 17A illustrates cell potential of a printed zinc, gel electrolyte,and MnO₂ microbattery as a function of percent depth of galvanostaticdischarge. The discharge rate was C/3.

FIG. 17B shows charge impedance spectra corresponding to equilibriumcell potentials of the three of the points illustrated in the plot ofFIG. 17A (1.267 V, 1.393 V, and 1.620 V) of a printed zinc, gelelectrolyte, and MnO₂ microbattery.

FIG. 18 shows the first eleven galvanostatic cycles of a cell containinga printed MnO₂ composite electrode, gel electrolyte, and zinc foilelectrode. A C/5 discharge rate was used. Between cycle 7 and cycle 9 asignificant discharge capacity increase is observed.

FIGS. 19A and 19B show a comparison of the potential of a printed MnO₂electrode, gel electrolyte, and zinc foil electrode cell. Thegalvanostatic charge (FIG. 19A, increasing cell potential) and discharge(FIG. 19B, decreasing cell potential) potentials of the third andeleventh cycle are compared.

FIG. 20 illustrates the galvanostatic cycling of a printed zinc, gelelectrolyte, and MnO₂ microbattery at a C/5 rate. Activation of thebattery occurs within the first 15 cycles. After more than 70 cycles nosign of performance degradation is visible.

FIG. 21 shows the percent of maximum discharge capacity extracted fromthe printed microbattery as a function of discharge current density.

FIG. 22 illustrates printed microbattery discharge time as a function ofdischarge power density.

FIG. 23 shows a series of self-discharge routines of the printedmicrobattery after charging. Potential decay at open circuit is plottedwith respect to time.

FIG. 24 is a series of self-discharge routines of the printedmicrobattery after charging. Potential decay at open circuit is plottedwith respect to the logarithm of time.

FIG. 25 shows a series of self-discharge routines of the printedmicrobattery after charging. Potential decay at open circuit is plottedwith respect to the square root of time.

FIG. 26 illustrates the Magnitudes of self-discharge of the printedmicrobattery due to charging. The slope of the potential decay at opencircuit is plotted with respect to the logarithm of time as a functionof cell potential.

FIG. 27 is a series of self-recovery routines of the printedmicrobattery after discharging. Potential recovery at open circuit isplotted with respect to the square root of time.

FIG. 28 is a series of self-recovery routines of the printedmicrobattery after discharging. Potential recovery at open circuit isplotted with respect to time.

FIG. 29 shows a series of self-recovery routines of the printedmicrobattery after discharging. The potential recovery of the battery atopen circuit is plotted with respect to the logarithm of time.

FIG. 30 shows the current response to potentiostatic control of aprinted battery. The float current is assumed to be the steady statecurrent achieved after holding the cell at a certain potential forextended times.

FIG. 31 is a plot of the charge passed due to leakage for two chargecycles as a function of cell potential.

FIG. 32 is a plot of the charge passed due to leakage for two dischargecycles as a function of cell potential.

FIG. 33 shows voltammograms of symmetric cells containing two adjacentlyprinted silver, nickel and aluminum current collector films, eachcovered in a printed gel electrolyte. The electrochemical instabilitiesof silver, nickel and aluminum in the gel electrolyte correspond withthe magnitude of current density detected for a given potential.

FIG. 34 shows voltammograms showing stability at various temperatures(25° C., 65° C., and 125° C.) of a cell containing two adjacentlyprinted aluminum foil current collector, each covered in a printed gelelectrolyte in accordance with the present invention.

FIGS. 35A through 35C show a schematic of printing process forelectrochemical capacitor.

FIG. 36 is a micrograph of a fabricated electrochemical capacitor crosssection.

FIG. 37 is a plot of cycle life vs. capacitance of the printedelectrochemical capacitor of FIG. 36

FIG. 38 is a plot of the charge and discharge cycle of the printedelectrochemical capacitor of FIG. 36.

FIG. 39 illustrates the pulsed behavior of the printed capacitor at 1mA, and 0.1 mA.

FIG. 40 illustrates an exemplary RFID chip incorporating the printedmicrobattery of the present invention.

FIG. 41 illustrates a schematic diagram for a method of generating aintegrated circuit with a print-on-green battery in accordance with thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

The preferred embodiments are illustrated in the context of a printablezinc electrochemical cell in which divalent ions travel through a gelelectrolyte. The skilled artisan will readily appreciate, however, thatthe materials and methods disclosed herein will have application in anumber of other contexts where divalent ion transport is desirable,particularly where simple and low-cost manufacturing is important.

In this disclosure, the terms “negative electrode” and “anode” are bothused to mean “anode.” Likewise, the terms “positive electrode” and“cathode” are both used to mean “cathode.”

Room temperature “Ionic liquids” are defined as a class of liquids thatare organic salts with low melting points (below 100° C.). Ionic liquidshave properties that include high ionic conductivity, very goodelectrochemical and temperature stability, and negligible vaporpressure. These enhanced properties and environmental benefits haveattracted diverse attention to room temperature ionic liquids aspotential replacements of volatile solvents and materials inmanufacturing, chemical reactions, separation, and electrolytes, to namea few. When ionic liquids are incorporated into polymer gels, they canform electrolytes that have liquid-like ion transport properties a feworders of magnitude greater than other polymeric or solid-stateelectrolyte systems. Such ionic liquid gel electrolytes can also bestructurally robust and can maintain physical separation between theelectrodes of an electrochemical cell even under compression.Furthermore, in ambient environments and room temperature conditions,the gel does not dry out or “sweat” as the ionic liquids are negligiblyvolatile.

“Multivalent” is herein defined as an atomic or molecular speciescarrying more than one full charge.

“Non-aqueous” is herein defined as a system that is largely free of thepresence of water, except in trace amounts as a residual contaminant.

Note that the power behavior of a battery can also be characterized byits rate performance, and is evaluated by the time (in hours) it takesto deplete a device of its maximum storage capacity (C). Note that thisterminology can be confusing, as C is also used to represent Coulombsand should not be confused when referred to as a rate of charge ordischarge. For example a battery that took 10 hours to completely drainwas discharged at a C/10 rate, while a quick discharge of 2C means thebattery was depleted in a half hour.

1. Electromechanical Cell

FIG. 1 is a schematic cross-section of an electrochemical cell 10according to an embodiment of the invention. The cell 10 comprises acathode 14 and anode 16 separated by a electrolyte layer 12. As shown inFIG. 1, current collectors 18 may be positioned at the open sides of theanode 16 and cathode 14 to provide proper electrical contact with load20. It is appreciated that the current collectors 18 are an optionalcomponent, and the cell 10 may comprise other configurations with orwithout current collectors 18.

As shown in FIG. 1 the electrochemical cell 10 can be attached to acircuit 22 to do work on an outside load 20. In one arrangement, theelectrochemical cell 10 is a battery cell. In another arrangement, theelectrochemical cell 10 is a rechargeable battery cell. In yet anotherarrangement, the electrochemical cell 10 may comprise a capacitor.

It is appreciated that the electrochemical cell 10 may be fabricatedusing any of the fabrication methods described below to comprise anumber of different structural arrangements. For example, the electrodesmay be oriented in a stacked configuration as shown in FIG. 1, or maycomprise a 2-dimensional planar configuration as shown in the cell 30 ofFIG. 2. In FIG. 2, cell 30 comprises an anode 16 positioned adjacentcathode 14 on substrate 68. Current collectors 18 may be use to provideelectrical contact between the anode 16, cathode 14, and the substrate.In this configuration the gel electrolyte 32 encapsulates, and providesseparation between, the anode 26 and cathode 14. It is appreciated thatthe device 10 of FIG. 1 may also be disposed over a substrate 68 asshown in FIG. 2.

Referring now to FIG. 3, a device 40 may comprise a custom connection ofan array of batteries 10 coupled to achieve tailored voltage, capacity,energy density, power density output.

The individual cells may be patterned as stacked sandwich (each cell 10patterned one on top of other, not shown), or the cells 10 can bepatterned in an open adjacent sandwich configuration where electrodesare adjacent to each other as shown in FIG. 3.

Positive and negative leads of each battery are accessible on asubstrate surface and can be connected via connectors 42, which maycomprise a conductive ink. In one embodiment, the conductive ink 42 maybe deposited using a variety of deposition methods, as will be furtherdetailed below, such as ink jet printing, screen printing, flexographicprinting, slot die coating, or the like.

As an alternative to a conductive ink, the connections 42 may be madevia a foil connection (e.g. aluminum, stainless steel, nickel foil,etc.) using foil die cutting, cold foil or hot foil printing methods.

In further alternative embodiments, connections 42 may be fabricated viaelastomeric connectors (ZEBRA, ACF tape), or via clamp connections,probe connections, wire bonding, etc.

Cells 10 may be connected so all cells are connected in series (positiveleads of one cell are connected to negative leads of other cells) to getmultipliers of cell voltages (i.e. one cell is 1.5V, two cells is 3V).

Cells 10 may be connected so all cells are connected in parallel(positive leads of one cell are connected to positive leads of othercell) to get multipliers of cell capacity (i.e. One cell has 5 mAh, twocells output 10 mAh). Mixed configurations of series and parallelconnections may also be made to get custom voltage and capacity output.

The sizes of each cell 10 may can vary, e.g. from dots ranging from 1 to5000 μm diameters, to modules from 0.25 to 500 cm², to large sheets from0.05 to 1,000 m².

Stacking of cells (not shown) may also be used to achieve custom voltageand parallel configurations. For series connection, cells may be stackedone on top of other by placing positive panel of one battery in contactwith the negative panel of another battery. For parallel connection,stacked cells may be separated by an insulator layer and an external busline can be used to connect positive terminals of cells (e.g. run downthe side of battery).

The gel electrolyte 12, 32 may be used as both a separator andstructural material (e.g. thickness/composition may be varied to provideadditional structural integrity, or may be used to encapsulate cell asshown in FIG. 2). The structural gel layer 12 may also be used to createnon planar form factor batteries, e.g. the gel electrolyte may bestructured to build up walls in which a trench is formed and back filltrench with other materials, such as an electrode.

In a preferred embodiment of the invention, the electrolyte layer 12, 32is a gel electrolyte as shown in the close-up view of electrolyte layerin FIG. 1. The gel electrolyte 12 contains salt cations 24, (Zn2+), andsalt anions and ionic liquid anions 28, the ionic liquid cations 26,which are imbibed in a polymer (dark lines). The gel electrolyte has apolymer network into which an ionic electrolyte liquid has been imbibed.In one arrangement, the polymer in the network is poly(vinylidenefluoride-hexafluoropropylene) (PVDF-HFP), PVDF and associated othercopolymers, PVA, PEO etc. Exemplary liquid electrolytes include a classof materials known as ionic liquids. One exemplary ionic liquidcomprises 1-butyl-3-methylimidazolium trifluoromethanesulfonate[C₉H₁₅F₃N₂O₃S]. An electrolyte salt appropriate for the divalent ormultivalent ions that are to be transported through the electrolyte gelis dissolved in the ionic liquid. In one arrangement, the salt is a zincsalt such as zinc trifuoromethanesulfonate [Zn(CF₃SO₃)₂], also known aszinc triflate or zinc bis(trifluoromethanesulfonate). The salt may alsocomprise other metals having multivalent ions, such as aluminum,magnesium, yttrium, or combination of the above.

The ionic liquids suitable for electrochemistry have low electricalconductivity (<5 mS/cm), large electrochemical stability windows (>1 V),ability to dissolve salts, and viscosities compatible with desiredprocessing methods, and may comprise cations such as imidazoliumvariants, pyrrolidinium variants, ammonium variants, pyridiniumvariants, piperidinium variants, phosphonium variants, and sulfoniumvariants, and anions such as chlorides, tetrafluoroborate (BF₄ ⁻),trifluoroacetate (CF₃CO₂ ⁻), trifluoromethansulfonate (CF₃SO₃ ⁻),hexafluorophosphate (PF₆ ⁻), bis(trifluoromethylsulfonyl)amide (NTf₂ ⁻),bis(fluorosulfonyl)imide (N(SO₂F)₂ ⁻). Further distinctions inelectrochemical, conductivity, and viscosity properties can be tailoredby the chain lengths of the cations.

In one embodiment, the liquid electrolyte has an ionic conductivitylarger than 1 mS/cm, and preferably ranging between 2 mS/cm and 3.5mS/cm, and more preferably between 2.3 mS/cm and 2.7 mS/cm.

In another embodiment, an ionic liquid gel electrolyte has an ionicconductivity larger than 0.01 mS/cm, or preferably ranging between 0.03and 3.5 mS/cm, and more preferably between 0.3 mS/cm and 2.7 mS/cm.

In yet another embodiment, the liquid electrolyte has a zinc saltconcentration between 0.2 and 0.75 M in ionic liquid, and preferablybetween 0.4 and 0.75 M, and more preferably between 0.45 and 0.65 M.

In another embodiment, a liquid electrolyte having a salt concentrationbetween 0.3 to 0.75M has an ionic conductivity ranging between 2.3 mS/cmand 2.7 mS/cm.

In a further embodiment, a liquid electrolyte having a saltconcentration between 0.4 to 0.75M has an ionic conductivity above 2.3mS/cm.

The preferred zinc salt concentration in the ionic liquid can also bedefined as the % of salt with respect to its solubility limit. Thesolubility limit of the zinc salt within the ionic liquid is defined asthe concentration of salt added to the ionic liquid at which no morezinc salt can be dissolved. In one embodiment, the preferred zinc saltconcentration is between 25% and 100% of its solubility limit, andpreferably between 50% and 95% of its solubility limit, and morepreferably between 60% and 88% of its solubility limit.

Furthermore, the ionic liquid electrolyte concentration in the polymergel can be defined as % weight of ionic liquid electrolyte in thepolymer gel. In one embodiment, the preferred % weight of ionic liquidelectrolyte to polymer is greater than 20%, and preferably rangingbetween 25% and 90%, and more preferably between 40 and 85%.

The gel electrolyte layer 12 acts as a physical and electronic separatorbetween the anode 16 and the cathode 14. Despite having mechanicalproperties similar to a solid material, the gel electrolyte 12 has iontransport properties very similar to a liquid electrolyte.

The ionic liquid gel electrolytes of the present invention have reducedflammability and less hazardous in comparison to typical organic andcorrosive electrolytes, making them inherently safer than traditionalelectrolytes used in commercial systems, especially in conditions ofpuncture (from nails, bullets, and other sharp objects) ripping,cutting, and other physical damage. Additionally, ionic liquid gelelectrolytes are unique in that ionic liquids have negligible vaporpressure and therefore do not evaporate or leak away even underprolonged use. By eliminating the problems of evaporation and leaking(also known as “sweating”), of the liquid component in the gelelectrolyte, expensive and complicated hermetic packaging is not needed,thus simplifying processing and reducing the cost of the battery systemimmensely.

In a preferred embodiment of the invention, the anode 16 comprises ametal which emits multivalent ions when undergoing an oxidation reactionwith the ionic liquid electrolyte. For example zinc metal forms zincions of divalent charge as a result of an oxidation reaction with theionic liquid electrolyte. The anode 16 may also comprise aluminum,magnesium, yttrium, or combination of metals that may include some orall of zinc, aluminum, and magnesium metals, or the like.

The anode material composition may also comprise of multiplemorphological features (e.g. zinc flakes and spherical particles andnanoparticles) to increase electrochemical capacity.

In one embodiment of the invention, the cathode 14 has, as a majorcomponent, a metal oxide. For example, the cathode 14 may comprisevanadium pentoxide (V₂O₅), manganese dioxide (MnO₂) particles, cobaltoxide (CoO_(x)) particles, lead oxide (PbO_(x)) particles, or the like.In yet another embodiment of the invention, the cathode 14 has, as asignificant component, particles of any metal oxide that can absorb andrelease ions that come from the anode.

In one arrangement, the cathode 14 also includes, as a component, apolymer binder, and optionally, electronically-conductive particles(e.g. high surface area carbons, activated carbons, or conductivenanoparticles), and optionally rheology-enhancing particles and polymers(e.g. titanium oxide powder and silica particles).

Cathode 14 composition may also be varied to utilize alternativemorphological forms of the conductive additives (e.g. graphites andflakey conductive particles) to provide better electrode conductivityand electrochemical properties for thick films >15 μm.

It is appreciated that for optimal cell performance, the cathode 14materials be matched with appropriate anode 16 materials. It isimportant that the cathode 14 contains, as a significant component,materials that can transfer and transmit ions that come from the anodethrough a combination of oxidation and reduction reactions. For example,the oxidation and reduction reactions for a cell 10 as shown in FIG. 1occur as provided in Equations 1 and 2 below:Zn←→Zn²⁺+2e ⁻  Eqn. 12e ⁻+(2MnO₂ ⁻)Zn²⁺←→Zn²⁺+2MnO₂  Eqn. 2

It is also important that the thermodynamic pairing of the anode andcathode materials form a desired electrochemical potential, manifestedin a measured cell voltage. For example, a zinc anode 16 may be coupledwith a MnO₂ cathode, and the typical cell voltage ranges between 1.1-1.6V.

As shown in FIG. 1 current collectors 18 are positioned adjacent to, andin electronic communication with the cathode 14 and anode 16. Examplesof useful current collectors 18 include, but are not limited to,stainless steel, zinc, gold, aluminum, and nickel.

For example, aluminum as a current collector 18 material was tested tohave electrochemical stability over −3 to 3V range when in contact withthe gel electrolyte of the present invention. Actual batteries usingaluminum foil as current collectors have been demonstrated. Similarly,batteries using nickel and stainless steel foils have also beendemonstrated separately as current collectors.

In addition, different forms of aluminum and nickel current collectorsare contemplated, e.g. foils, nanoparticle ink, composite slurry,electrodeposited coating, and vapor deposited metal.

Cold foil printing, hot foil printing, or kiss-cut die cutting(processes generally used extensively in the printing, lamination, andtape conversion industry) may also be used to pattern metal foilconductive traces on substrates (such as paper, plastic, fabric). Theseprocesses are highly scalable, cost-effective, and high throughputmethods for patterning metal foils on non-conductive substrates orbackings.

Foil current collectors 18 would preferably be used 1) in situationswhere high amounts of bending and creasing and ruggedness are desired,2) if paper/plastic/fabric substrates are used to eliminate an inkprinting step, or 3) low cost applications.

There are many possible kinds of substrates 68 that can be used tosupport printing of the electrochemical cell. Examples of possiblesubstrates include, but are not limited to, paper (e.g. cardstock ordifferent types/weaves/thicknesses of paper), polymeric or plasticmaterials (e.g. polyethylene tetrephthalate or polyester (PET),polyethylene, polypropylene, Kapton, polyimide, polyester ether ketone(PEEK), polyurethane, polydimethysiloxane or other silicone resins),fabric of various weaves and meshes (e.g. nylon, cotton, denim) silicon,printed circuit board (e.g. cured epoxy resin substrates, FR4, andflexible circuit boards), glass, metal foil, or combination thereof(e.g. fabric with plastic backing). In one arrangement, the substrate isa material that can be folded into any shape as required for theapplication. In one arrangement, a device such as a microprocessor or aMEMS device can be used as the substrate 68. Any of the substratesmentioned above may also have an adhesive backing that will allow forintegration of battery onto a surface.

The substrate 68 and electrode layers are preferably configured towithstand bending and levels of curvature from increasing to largecurvature radii (e.g. wrist watch curvatures, and curvatures experiencedin rolling processes).

The gel electrolyte 12 may also comprise of component compositionsconfigured to withstand environmental levels of stability. For example,cell 10, 30 may withstand high temperatures, e.g. up to 150° C. forextended exposure (without polymer degradation), and even higher temps(like solder temperatures, e.g. 200° C. to 300° C.) for very shortamounts of time (several seconds). Cell 10, 30 may withstand lowtemperatures, e.g. down to −20° C. for consumer electronics and down to−40° C. for industrial applications, and low and high humidity.

Additional packaging (not shown) may also be provided with encapsulationtypes and methods, such as: dip coating in polymers and/or elastomerssuch as silicone, single sided printing of encapsulation ink material,double sided printing of encapsulation ink material, hot lamination (thecell 10 of the present invention was tested to withstand the highpressure and temperature associated with this process), polymerlamination with an adhesive, metal foil pouches hot pressed at edges,hard packages, e.g. metal cases, and conventional battery packages.

One or more of the various cell 10 layers (e.g. gel electrolyte 12,electrodes 14, 16, current collectors 18) may be formulated into an inkfor fabricating an electrochemical cell by printing at least some of thelayers. Desirable materials can be mixed together to form, for example,solutions, suspensions, melts, or slurries, which can be used as “ink”in the printing process.

Various deposition methods may be employed, e.g. direct write printing,screen printing (e.g. Atma, M&R, Colt), flexographic printing (Dai'sMachinery, Line O Matic), gravure printing, dispenser printing, ink jetprinting (e.g. Fuji Dimatix), slot die coating.

FIG. 4 and FIGS. 5A through 5D illustrate a method of printing amicrobattery using dispenser printing in accordance with the presentinvention. It is appreciated that other printing/deposition methods mayalso be used, and that the direct write dispensing method of FIGS. 4 and5A through 5D are illustrated for exemplary purposes only.

Direct write dispenser printing comprises a method for additivelydepositing a variety of materials, including slurries, solutions, andsuspensions, generally referred to as “inks.” Direct write dispenserprinting is a flow-based method of direct write patterning with theability to deposit inks at room temperature and ambient conditions, allthe while generating negligible materials waste and requiring minimalenvironmental overhead. In comparison to conventional microfabricationtechniques, which utilize subtractive processes such as lithography andetching, the number of process steps, energy demanded, and wastegenerated is significantly less.

The material compositions of the present invention may be printed on tovarious surfaces using the dispenser printer system 100 and printer 102shown in FIG. 6. The ink is loaded into a syringe 66, extruded through ahollow needle of predetermined dimensions, and written onto a substrate68 via a succession of drops, or “shots.” The drop size is determined bythe needle's dimensions, ink rheology, and applied pressure. Theresulting printed film 70 morphology depends on the dimensions of theextruded drops as well as the traversing distance, speed, and timebetween shots. The motion of the three-axis stage 104 on which thesyringe 66 and substrate 68 are mounted, along with the pressure appliedfrom a pneumatic controller 108, generates the dimensions and shapes ofthe deposited films.

Pneumatic pressure is applied using a controller 110 (e.g. MusashiML-808FX) that is capable of 2-50 kPa output. Disposable syringe needles66 of 16-30 Ga (0.15 to 1.35 mm inner diameter) are used to print theinks; tips with inner diameters as small as 0.05 mm can be fabricated bypulling capillary glass tubes using a glass pipette puller. A variety oftips with different needle sizes may be used according to thecomposition of the layer being deposed and the desired layer dimensions.As a general rule, the smallest diameter needle that a slurry can beconsistently printed through must be at least an order of magnitudelarger than its largest particles. Depending on the ink, preparation mayinclude a combination of ball milling the particles, physical mixing(magnetic stirrers, paint shakers, vibrating surfaces) and ultrasonicmixing (with a water bath or wand).

With the assortment of needle sizes and wide span of pneumatic pressuresthat can be applied, the dispenser printer is able to process a varietyof inks into a range of printed feature sizes. All the equipment iscontrolled and automated through computer 12 and software implemented ona personal computer.

FIG. 4 illustrates ink preparation process in accordance with thepresent invention. At step 52 a gel polymer network is provided. In onearrangement, the polymer in the network is poly(vinylidenefluoride-hexafluoropropylene) (PVDF-HFP). At step 54 the activeparticles 62 are mixed with the gel polymer 60 to create the ink 64. Theactive particles may vary according to the desired layer that is beingprinted (e.g. gel electrolyte 12, anode 16, cathode 14 or currentcollector 18 (if printed). Various solvents may also be added to changethe rheology of the ink or change the working time of the ink so it ismore compatible with different printing processes, for example,n-methyl-2-pyrrolidone (NMP), Dimethyl Sulfoxide (DMSO), 2-Pyrrolidone,N-ethyl-2-pyrrolidone (NEP), Dimethyl Formamide (DMF), or Acetone. Thesolvent or “vehicle” is later evaporated from the film.

The ink 64 is then placed in a syringe needle 66 at step 58 to print thedesired layer 70.

FIGS. 5A through 5D show an exemplary method for fabricating a printedcell in accordance with the present invention. At step 82 shown in FIG.5A, a substrate 68 (e.g. Nickel) is provided. Optionally, where a firstcurrent collector is used, a current collector (not shown) may beprinted onto the substrate. In other arrangements, no first currentcollector is used, and at step 84 the first electrode layer 14 (e.g.MnO₂ cathode) is printed directly onto the substrate 68. Electrode layer14 is printed onto the substrate 68 as a first ink dispenser 90 passesover the substrate 68. Where a current collector is used, the firstelectrode layer 14 is deposited on top of that layer.

At step 86 shown in FIG. 5C, a gel layer 12 is printed onto the firstelectrode layer 14 as a second ink dispenser 86 passes over the firstelectrode layer 12. In one arrangement, the electrolyte 12 is a gelelectrolyte, preferably comprising ionic liquids mixed with a polymernetwork into which the electrolyte liquid has been imbibed. Anelectrolyte salt appropriate for the divalent/multivalent ions that areto be transported through the electrolyte is dissolved in the ionicliquid.

At step 88 shown in FIG. 5D, a second electrode layer 16 (e.g. zincanode) is printed onto the electrolyte layer 12 as a third ink dispenser94 passes over the electrolyte layer 12. It is appreciated that thefirst electrode layer 14 can be either a positive electrode or anegative electrode, and the second electrode layer 16 is the oppositetype from the first electrode 14. That is, if the first electrode 14 isa positive electrode, then the second electrode 16 is a negativeelectrode, and vice versa. Materials for positive electrodes andnegative electrodes have been discussed above.

In one arrangement, printable materials for electrodes are slurries ofactive electrode material particles mixed with a polymer binder(s), aremovable solvent, and optional additives. In one embodiment of theinvention cathode chemistries may comprise a metal oxide such asvanadium pentoxide particles or manganese dioxide particles or bothkinds of particles as the active cathode material particles. In oneembodiment, the anode chemistries have zinc particles as the activeanode material particles.

It is appreciated that not all layers of the electrochemical cell 10 arenecessarily printed layers. It is possible to replace one or moreprinted layers with pre-formed films. In an exemplary embodiment, a zincfoil is used for the negative electrode layer instead of printing thelayer with a slurry that contains zinc particles. Additionally, thecurrent collectors may comprise a cold or hot foil printed aluminum foilor vapor deposited metal traces. It is also contemplated that the layersmay use other deposition methods, such as coating, etc.

After each layer has been deposited in the desired electrochemical cellstructure, the layer can be dried. Each subsequent layer is deposited inthe desired arrangement and then dried. The drying process removes thesolvents that may be components of the slurries used in one or morelayers, thus leaving a layer that is a solid, layered film. After alllayers are arranged, the entire electrochemical cell structure may bedried to remove any residual evaporative solvents. In one arrangement, alayer or the cell structure is dried at room temperature for about 1-15minutes and then at 60°−90° C. for about 3-30 minutes. In anotherarrangement, a layer or the cell structure is dried using a vacuum oven.In yet another arrangement, a layer or the cell structure is dried usingan infrared or heat lamp.

In one arrangement, the substrate 68 can be removed after theelectrochemical cell has been fabricated.

In comparison to currently-available, thin-film batteries, the printablezinc electrochemical cell 10 of the present invention offers severalunique advantages. One important advantage is that the printingmaterials and methods for fabricating electrochemical cells, asdescribed above, can be performed at room temperature and under ambientconditions. That is, no special vacuum or forming gas atmosphere is usedto fabricate the cells. Thin film battery vapor deposition technologyrequires a high temperature (>400° C.) annealing step to formcrystalline phases of the thin-film deposited electrodes. Such ambientconditions make it possible to consider manufacturing, materials, andprocess options that have not been possible before. For example,temperature-sensitive substrates such as polymer films or paper can beused as there is no high-temperature annealing step in the process.

Current thin film battery vapor deposition technologies often haveproblems with building thick electrode films due to high stresses thatdevelop in films during thin-film processing. Thus, the thicknesses ofsuch electrode films can be no more than a few microns, severelylimiting the energy storage capacity with respect to the footprint areaof the battery. In contrast, the printable electrochemical cells 10 ofthe present invention can be printed with much thicker electrodes—atleast one to two orders of magnitude thicker than thin filmmicrobatteries—and therefore can achieve much higher areal energydensities.

Finally, nearly all thin film batteries, such as lithium or lithium-ionthin film vapor deposited batteries or zinc-based alkaline and acidicsemi-printed batteries, are either extremely sensitive to moisture orutilize a liquid component, and therefore great efforts to seal thecells hermetically are needed. In comparison, the chemistry disclosedherein is physically solid state and much more environmentally stable.The gel electrolyte 12 is non-aqueous, and contains no corrosivecomponents, and does not leak or dry out even after prolonged cell use.Thus the printed cells 10 can be used without the robust and expensivehermetic packaging that is required in typical commercial cells.

As an added benefit, no expensive vacuum equipment is needed tofabricate or process the battery. All in all, the processes andchemistries described herein are much simpler than standard sputter orvapor deposition or liquid handling thin film methods that are currentlythe industry standard. Such simplicity makes it possible to produceelectrochemical cells with many more options and at a lower cost thanhas been possible before.

This rechargeable battery has a nominal voltage between 1.1-1.6Vdepending on the cathode electrode chemistry, and may be operatedbetween 0.7-3 V.

2. Experimental Results

Generally, the study and use of ionic liquids in batteries predominantlyhas been focused on lithium and lithium-ion battery systems, and haslargely disregarded its application to non-lithium battery chemistries,especially electrode pairs traditionally utilizing aqueous electrolytessuch as zinc-carbon and zinc-manganese dioxide systems. Traditionalalkaline and acidic zinc-based batteries undergo electrochemicalreactions which require the presence of water, while lithium-basedbattery chemistries utilize non-aqueous, aprotic, organic electrolytes.Historically there have been minimal efforts to apply historicallywell-known organic liquid electrolytes used in commercial lithium andlithium-ion batteries (such as propylene carbonate, ethylene carbonate)to zinc-based battery systems. Therefore, as battery electrolytematerials research has shifted towards the study of ionic liquidelectrolytes, this effort has concentrated on lithium-based chemistriesand has been overlooked for zinc-based systems. To date, the transportproperties and mechanisms of divalent or multivalent ions in ionicliquid solvents applied to battery systems are unknown and unutilized.Furthermore, the electrochemistry of zinc electrodes in combination withnon-aqueous systems is less understood. In general, the relative sizeand charge of multivalent ions would be greater than monovalent ions(zinc ions are bigger than lithium and contain double the charge). As aresult it would be expected that transport of zinc ions in the gelelectrolyte would be significantly slower than in lithium systems, andthe transport mechanisms more complex due to its dual charge. However,when measured, the transport of zinc ions in an ionic liquidelectrolyte, specifically the ionic conductivity, was demonstrated to beas much as an order of magnitude greater than in an analogouslithium-ion ionic liquid electrolyte system. This suggests that becauseof its unique properties, the transport mechanisms within the gelelectrolyte are different for zinc ions than with lithium ions. This wasan unexpected result.

In an analogous lithium ion battery using a similar gel electrolytematerial, when exposed to ambient air conditions, the battery was unableto function for more than 24 hours. Part of what was assumed toattribute to this was that the gel electrolyte is made of a constituentthat is very hygroscopic, rapidly absorbing moisture from theenvironment. When a similar zinc battery was constructed with the gelelectrolyte material, the battery was tested in the same ambient airconditions but was able to survive and perform without any signs ofdegradation over many months (estimated 3-4 months). This was also asurprising result.

The following examples provide details relating to composition,fabrication and performance characteristics of block copolymerelectrolytes in accordance with the present invention. It should beunderstood the following is representative only, and that the inventionis not limited by the detail set forth in these examples.

FIG. 7 illustrates the viscosity of a slurry having representativeformula for a battery electrode and polymer solution as a response toshear rates applied to the inks. The polymer solution is composed of arepresentative formula for the gel electrolyte. The viscosities of theinks were measured with respect to varying shear rates applied by aRheometric ARES rheometer [TA Instruments].

As shown in FIG. 7, the polymer solution displays a relatively constantviscosity for the shear rates applied, demonstrating Newtonian behavior(where the viscosity is insensitive to changes in shear rate). For shearrates greater than 0.2 1/s, the composite slurry ink viscosity decreaseslinearly with increasing shear rate on a log-log plot. The minimum andmaximum shear rates applied to the ink by the printer are determined andthen related to the corresponding dimensions of the printed feature.This was calculated by measuring the flow rate of ink through thesmallest and largest syringe tips as a function of applied pressure.

In FIG. 7, the ranges of shear rates and corresponding printed featuresizes applied by the dispenser printer are bracketed for both inks. Forexample, for a dispenser shot time of 10 ms and the smallest pneumaticpressure of 20 kPa, the polymer electrolyte solution extruded from a 16gauge needle was visually recorded with an orthogonally mounted camera,and then the drop volume was determined using image analysis software.The volume of ink was approximated as 1.18 mm³, with the shear rateexperienced by the ink under these conditions was 491.9 1/s, resultingin a dot pitch of 150 μm. This experiment was repeated for the smallestand largest gauge disposable needles available that could extrude theink (between 16-30 gauge, respectively), and with the lowest and highestpneumatic pressures applied by the controller.

It is appreciated that the viscosity data shown in FIG. 7 are specificto dispenser printing processes. Viscosity may vary depending on thedeposition process that is used, e.g. the desired viscosity would varyfor screen printing or other processes.

As seen in FIGS. 8A and 8B “grains” in the gel are observed to enlargesignificantly in volume with the increased incorporation of a liquid(from 25 to 60 wt. % ionic liquid electrolyte). The gels of thesecompositions essentially act like flexible yet mechanically strongfilms, and can be compressed substantially without damage to thestructure or oozing of the liquid phase. No visible “sweating” of theionic liquid from the gel could be discerned even after extended use orshelf life. Exceeding 75 wt. % ionic liquid, the polymer is unable toaccommodate the liquid, with a significant diminishment in the film'sgrain sizes and visible separation of the polymer and ionic liquidconstituents.

The electrochemical and transport properties of an ionic liquidelectrolyte and its compatibility with a zinc ion conducting batterywere also investigated. 1-butyl-3-methylimidazoliumtrifluoromethanesulfonate (BMIM+Tf−) ionic liquid was used because ofits availability, affordability, and its compatible anion with a zincsalt (zinc trifluoromethanesulfonate). However other ionic liquids andsalt pairs may also be considered for this electrochemical system; forexample, ionic liquids with reduced viscosities and more stable anionscould be used for significant improvements in performance. Theelectrochemical properties of the BMIM⁺Tf⁻ ionic liquid with zinc saltconcentrations varying between 0-0.75 M were compared. Note that beyond0.75 M, the zinc salt was no longer completely soluble in the ionicliquid. In an analogous lithium electrolyte solution, the lithium saltlithium trifluoromethanesulfonate was soluble to approximately 1.4 Mconcentration in the same ionic liquid.

An electrolyte is only effective if it is stable within the operatingelectrochemical potential range of a device. Linear sweep voltammetry(LSV) experiments were performed on each of the ionic liquidelectrolytes to determine its potential range of electrochemicalstability. By applying a sweeping voltage at a rate of 5 mV/s to cellscontaining the ionic liquid electrolytes between zinc and a stainlesssteel blocking electrode, the anodic stability of the electrolytes wasdetermined by monitoring the resulting current density (FIG. 9). Withrespect to the zinc electrode, all concentrations showed negligiblecurrent densities between 0 and 2.7 V, and therefore all electrolytescan provide the requisite electrochemical stability for a batteryoperating between the device voltages of 1-2 V. The measured currentdensities of the cells above 2.7 V rose accordingly with the increasedzinc salt concentrations of the electrolyte; for the ionic liquidsincorporating zinc salt, the current densities exceeded 1 mA/cm².

Ionic conductivity and viscosity comparisons of the ionic conductivityand viscosity properties of the ionic liquid electrolytes with zinc saltconcentrations between 0-0.75 M were measured. The viscosities of theionic liquids were measured with a Brookfield DV-III+ with a smallsample, small volume adapter. Ionic conductivity properties wereextracted via electrochemical impedance spectroscopy (EIS) measurementsof symmetric cells containing the liquid electrolyte sandwiched by two(see FIG. 9). Electrochemical potential stability ionic liquidelectrolytes with 0 to 0.75 M zinc salt concentrations. The occurrenceof a large magnitude current density corresponds to electrolytedecomposition blocking stainless steel electrodes. The neat BMIM+Tf−ionic liquid exhibited an ionic conductivity of 3.15 mS/cm.

With increased addition of zinc salt to the ionic liquid, a decrease inionic conductivity was measured. This behavior is counterintuitive, asit would be assumed that an increase in ion concentration in the systemwould result in an increased ionic conductivity. Conversely, the addedion concentration in an ionic liquid reduces overall ion mobility in thesystem, as could be detected with a significant viscosity increase;hence an inverse relationship between the two properties is detected andillustrated in FIG. 10.

Ionic conductivity is a function of ion concentration and mobility.Though the concentration of ions in the ionic liquid electrolyte isincreased with greater salt concentration, the mobility of the system isgreatly reduced.

Similarly, the electrolyte's zinc ion diffusion coefficients measuredusing restricted diffusion methods showed a diminishing trend withincreased zinc salt concentration. This trend can also be attributed tothe escalation of electrolyte viscosity with added zinc saltconcentration. A comparison of these transport property trends with ananalogous lithium ion. ionic liquid system can provide additionalempirical observations on how the divalent nature and relative size ofthe zinc ion may affect its behavior in an ionic liquid electrolyte.Note that the lithium electrolyte is solely composed of lithium ions(Li⁺), imidazolium-based cations (BMIM⁺), and trifluoromethanesulfonateanions (Tf⁻); the zinc electrolyte constituents are zinc ions (Zn²⁺),BMIM⁺ cations, and Tf⁻ anions.

The ionic conductivities of the BMIM⁺Tf⁻ ionic liquid with varyingconcentrations of lithium trifluoromethanesulfonate salt were measuredin the same manner described with the zinc system and plotted in FIG.11. At salt concentrations below 0.3M, both systems showed similar ionicconductivities, but as more salt was added to the electrolytes, theirbehaviors diverged. In both electrolytes, the ionic conductivitydecreased with increasing salt concentration, but the conductivity ofthe lithium system diminished at a more rapid rate. This observation iscounterintuitive for two reasons; firstly the size of a lithium ion issmaller than a zinc ion (the ionic radiuses are 0.68 nm and 0.74 nm,respectively), therefore we would expect reduced ionic conductivity inthe zinc system due to the sluggish transport of the larger zinc ions.

The differences in ionic conductivity behaviors with respect to soluteconcentration for the lithium and zinc ionic liquid electrolyte systemsdepend heavily on the population of trifluoromethansulfonate ions in theelectrolyte. The lithium-based ionic liquid electrolyte differs from thezinc-based ionic liquid electrolyte due to the different valences of thesolute cations. For every mole of zinc salt, Zn+(Tf−)2, to a givenvolume, the volume will contain two moles less of BMIM+Tf−. For one moleof lithium salt, Li+Tf−, to the same volume, there will be only one moleless of BMIM+Tf−. These statements are possible assuming that thecationic volumes in the electrolyte are equal. As a result, thezinc-based ionic liquid electrolyte demonstrates higher ionicconductivities and lower viscosity than the lithium-based ionic liquidelectrolyte.

A comparison of the diffusion coefficients of the active ions withrespect to salt concentration in the ionic liquid electrolyte wasconducted. From the data exhibited in FIG. 12 taken using the restricteddiffusion measurement method, lithium ions are shown to have diffusioncoefficients an order of magnitude greater than zinc ions in the ionicliquid electrolyte for all salt concentrations. This suggests thatthough the [Zn²⁺][BMIM⁺][Tf⁻] system exhibits an overall higher ionicconductivity than [Li⁺][BMIM⁺][Tf⁻], the zinc ion transport mechanism inthe ionic liquid may differ from that of a lithium ion. With a divalentcharge, a zinc cation may interact more strongly with neighboring Tf⁻anions, creating ion complexes tethering pairs, trios, and plausiblymore anions. These ion complexes however, may be freeing the large[BMIM⁺] cations in the [Zn²⁺][BMIM⁺][Tf⁻] system, allowing their rapidtransport within the electrolyte, and as a consequence, contributing tohigher overall ionic conductivities, and altering the divalent zinccation transport mechanism through the ionic liquid electrolyte mediumin comparison to a monovalent ion.

The reversibility of the zinc dissolution (Zn→Zn²⁺+2e⁻) and conversedeposition reactions across a zinc electrode and electrolyte interfaceas a function of electrolyte concentration were determined by comparingtheir respective current densities measured using cyclic voltammetry ofsymmetric cells sandwiching the electrolyte between two zinc electrodes.A scan rate of 10 mV/s was used. The voltammograms of ionic liquidelectrolyte with zinc salt concentrations ranging from 0 to 0.75 M aredisplayed in FIG. 13. The largest magnitudes of the anodic (positive)and cathodic (negative) current densities occur at 0.73 V and −0.69 V,and correspond to the maximum rate of dissolution and depositionoccurring at the working electrode, respectively; the magnitude of thecurrent density peaks are 2.21 mA/cm² and −2.63 mA/cm². The efficiencyof the reaction, calculated by comparing the ratio of the anodic andcathodic current densities, is 84%. The voltammogram illustrates thatzinc ions are able to transport through the ionic liquid electrolyte andthen plate and strip onto or away from an zinc electrode. Therefore theionic liquid is a candidate electrolyte for a zinc ion battery. Withadded zinc salt, the maximum anodic and cathodic current densitiesshowed an increasing trend.

The cycle magnitudes of the anodic peak current densities for the ionicliquid electrolytes with varying zinc salt concentrations are shown inFIG. 14. The magnitudes of the dissolution reaction were recorded formultiple cycles. The electrolytes with concentrations between 0.1-0.5 Mshowed relatively similar peak anodic current densities when cycledrepeatedly; for 0.75 M zinc salt concentration, the electrolyte wasunable to demonstrate steady cycling behavior, and a decrease ofapproximately 70% in the peak anodic current density occurred within thefirst seven cycles. This trend was also observed in the cathodic sweep.From these studies, it was empirically determined that a 0.5 M zinc saltconcentration in BMIM+Tf− exhibited desirable electrochemical andphysical properties and was used as the ionic liquid electrolyte in allfuture experiments.

The bulk transport properties of the ionic liquid gels were analyzed todetermine an optimal gel electrolyte composition. The ionicconductivities of the gels were measured with EIS on symmetric cellsformed by casting the gels between two blocking stainless steelelectrodes. The gel film thicknesses were measured subsequently withdigital calipers and verified using microscopy. The room temperatureionic conductivities of the gels (FIG. 15) were found to increase withhigher ionic liquid electrolyte concentration. A gel composition of 1:1ionic liquid electrolyte to PVDF-HFP weight ratio was determined to haveoptimal mechanical integrity and transport properties. At thiscomposition, the room temperature gel ionic conductivity (0.37 mS/cm) isreduced an order of magnitude lower than the neat ionic liquid (2.4mS/cm), however the gel is considered fairly conductive compared to drypolymer (0.01 mS/cm) and glassy (<10 μS/cm) electrolyte

Zinc ions were demonstrated to be able to travel through an ionic liquidelectrolyte, with an optimal formula that maximized its transport,viscosity, and electrochemical properties. The zinc salt and ionicliquid solution was swelled into a polymer binder to form a gelelectrolyte. The printable gel retains liquid-like ion transportproperties, but acts like a solid film that can be flexed and compressedwithout damage. Furthermore, because of its negligible volatility, theionic liquid does not “sweat” from the gel and is able retain itsproperties over long times even when exposed to the ambient.

A micrograph of the cross section of a printed microbattery 10 is shownin FIG. 16. Each film was printed and then dried at 60° C. for 15 to 30minutes. Square test cells were printed within 0.25 cm² footprint areasand had total thicknesses between 80 and 120 μm. For this configuration,the zinc film 16 serves both as the electrode but also as its owncurrent collector. Nickel foil was used as the current collector of themanganese dioxide electrode 14 as well as the substrate upon which thebattery was printed on. Although it is well within the scope of thistechnology to utilize a printed nickel current collector to achieve afully printed battery, the current microbattery configuration emulatesthe likely circumstance in which the microbattery will be printed onto apatterned substrate such as a PCB board in which the bottom currentcollector is already fabricated through previous processes such as vapordeposition.

A microbattery cell was fabricated as follows: Electrode films weredeposited as slurries composed of powders, additives, a common polymerbinder, and a removable solvent that tailors the viscosity of the ink.The polymer binder and solvent used were poly(vinylidenefluoride-hexafluoropropylene), (PVDF-HFP from Kynar Flex 2801), andn-methyl-2-pyrrolidone (NMP from Sigma Aldrich), respectively. The zincelectrode was 95 wt % zinc powder (Alfa-Aesar) and 5 wt % PVDF-HFP.Manganese dioxide (MnO₂) electrodes were 90 wt % activated MnO₂ powder(Alfa Aesar), 6 wt % acetylene black conductive filler (Alfa Aesar), and4 wt % PVDF-HFP. The gel electrolyte was a 1:1 mixture of PVDF-HFP and a0.5 M solution of zinc trifluoromethanesulfonate (Zn⁺Tf⁻) salt dissolvedin a 1-butyl-3-methylimidazolium trifluoromethanesulfonate (BMIM⁺Tf⁻)ionic liquid. The inks were printed into designated patterns, andmultiple films were deposited successively to form a stackedmicrobattery configuration as shown in FIG. 16.

The cell was 0.49 cm² in size, and the electrode dimensions rangedbetween 50 and 80 μm. Electrolyte thicknesses were between about 15 and30 μm. The zinc slurry served as both the electrode and its own currentcollector, while a nickel foil substrate was used as the currentcollector of the manganese dioxide electrode.

After printing the stacked battery structures, the devices were allowedto equilibrate over 24 hours before characterization. The typical cellpotential evolution of the printed battery as a function of depth ofdischarge for a galvanostatic discharge rate of C/3 is shown in 17A. Theworking range of this battery lies between 1 and 2 V. The cell'simpedance spectra from the discharge routine were recorded. Of thephenomena contributing to the cell impedances, the mixed contributionsof the charge transfer kinetics and diffusion appear to be mostprofoundly affected by the cell's steady state voltage. This issupported by the EIS spectra of the charge scans compared in FIG. 17B.With increasing cell potential from 1.267 to 1.620 V, the chargetransfer and diffusion semi-circles elongate and expand with the sametrend as the discharge scan.

An MnO₂ composite electrode test structure was also galvanostaticallycycled against a zinc foil electrode. For many cells that were tested,it was observed that with a moderately slow charge and discharge rate(between C/2 to C/5), an activation process occurred within the initialcycles.

This is usually manifested in a significant capacity increase within thefirst 25 galvanostatic cycles. As seen in FIG. 18, the printed battery'sdischarge capacity increased more than two-fold between cycles 7 and 9,and maintains this storage capacity with further cycling. A comparisonof the charge and discharge curves for cycle 3 and cycle 11 are shown inFIGS. 19A and 19B. Note that when comparing the two cycles, not only docycle 11's charge and discharge potential curves lengthen two-fold withdepth of discharge, the shape of the curve is also altered: a sharp kneeis visible upon charge at 1.52 V, and a steeper vertical decline occurswhen switching between charge and discharge. The former feature suggeststhat the manganese dioxide electrode undergoes an activation processinduced by the insertion of zinc ions, which may be causing thecrystalline material to increase in volume or undergo a phase change.This phase change is accompanied by an enhanced accessibility tointerfacial sites upon which zinc ions may react, and therefore anincrease in storage capacity as well as a larger ohmic drop whenswitching current directions. The latter feature, an increased ohmicresistance in the cell with cycling, is consistent with the activationphenomenon; the amorphous phase of manganese dioxide may be moreelectronically resistive than the crystalline phase or a morphologychange may have occurred, causing a disruption in electronic pathwaysthrough the electrode film.

The cells were cycled galvanostatically at discharge rates of C/5, andas seen in FIG. 20, over 70 cycles were achieved without sign ofperformance degradation. This printed battery also showed similaractivation behavior of its manganese dioxide electrode within the first15 cycles. Test cells achieved an average of 1 mAh/cm² in capacity and1.2 mWh/cm² in areal energy density

Initial studies on the rate performance of the printed battery are shownin FIG. 21. Deep galvanostatic discharge capacities were measured forvarying discharge current densities, and normalized with respect to itsmaximum capacity (approximately 1 mAh/cm²). The cells were charged usingthe same algorithm: a constant current charge of 0.1 mAh/cm² followed byholding the cell at a constant voltage of 1.8 V for 3 hours. Cells weredischarged between 1.8 to 0.3 V. The maximum achievable storage capacityis attained for discharge current densities between 0.1 and 1 mA/cm²,which corresponds to approximately C/2-C/7 rates. For current densitieshigher and lower than this range, the extractable discharge capacitydiminishes due to the high cell impedance for the former, whileself-discharge and leakage mechanisms dominate the latter. Formicrodevice applications, it is unlikely the microbattery will bedischarged at a rate lower than C/10, even if used in conjunction withan energy harvesting device. On the other hand, high rates of dischargeare likely, and the rapid decrease in usable capacity for any ratesabove 1C prevents this device from suitably addressing the exacting highpower pulses typically demanded from microdevices such as wirelesssensors. A load leveling capacitor may alleviate such high power densitydemands, and protect the battery from detrimental pulsing.

Accordingly, it the current density output of the device was shown torange between 0.001 mA/cm² and 100 mA/cm².

In one embodiment, the environmental stability of ionic liquid gelelectrolyte exposed to the ambient environment at room temperature 20°C. outputs a measureable current density of less than 25 μA/cm², orpreferably less than 15 μA/cm², and is maintained at least greater than1 week of exposure, or preferably greater than 3 months of exposure, andmore preferably greater than 6 months of exposure.

In one embodiment, the environmental stability of ionic liquid gelelectrolyte exposed to elevated temperatures between 20° C. and 45° C.outputs a current density of less than 50 μA/cm², or preferably lessthan 25 μA/cm², or more preferably less than 15 μA/cm², and ismaintained at least greater than 1 day of exposure, or preferablygreater than 1 week of exposure, and more preferably greater than 3months of exposure.

In one embodiment, the environmental stability of ionic liquid gelelectrolyte exposed to elevated temperatures between 45° C. and 90° C.outputs a current density of less than 75 μA/cm², or preferably lessthan 50 μA/cm², or more preferably less than 40 μA/cm², and ismaintained at least greater than 1 day of exposure, or preferablygreater than 1 week of exposure, and more preferably greater than 1month of exposure.

In one embodiment, the environmental stability of ionic liquid gelelectrolyte exposed to elevated temperatures greater than 90° C. outputsa current density of less than 75 μA/cm², or preferably less than 50μA/cm², and is maintained for at least greater than 1 millisecond ofexposure, or preferably greater than 1 hour of exposure, of morepreferably greater than 1 day of exposure.

In one embodiment, the environmental stability of ionic liquid gelelectrolyte exposed to depressed temperatures between −20 to 20° C.outputs a current density of less than 50 μA/cm², or preferably lessthan 25 μA/cm², or more preferably less than 15 μA/cm², and ismaintained at least greater than 1 day of exposure, or preferablygreater than 1 week of exposure, and more preferably greater than 3months of exposure.

In one embodiment, the environmental stability of ionic liquid gelelectrolyte exposed to elevated temperatures less than −20° C. outputs acurrent density of less than 75 μA/cm², or preferably less than 50μA/cm², and is maintained for at least greater than 1 millisecond ofexposure, or preferably greater than 1 hour of exposure, of morepreferably greater than 1 day of exposure.

In one embodiment, the environmental stability of ionic liquid gelelectrolyte exposed to relative humidity levels between 30-80% outputs acurrent density of less than 75 μA/cm², or preferably less than 50μA/cm², or more preferably less than 25 μA/cm², and is maintained atleast greater than 1 day of exposure, or preferably greater than 1 weekof exposure, and more preferably greater than 3 months of exposure.

In one embodiment, the environmental stability of ionic liquid gelelectrolyte exposed to relative humidity levels greater than 80% outputsa current density of less than 75 μA/cm², or preferably less than 50μA/cm², and is maintained at least greater than 1 day of exposure, orpreferably greater than 1 week of exposure, and more preferably greaterthan 1 month of exposure.

In one embodiment, the environmental stability of ionic liquid gelelectrolyte exposed to relative humidity levels less than 20% outputs acurrent density of less than 75 μA/cm², or preferably less than 50μA/cm² or more preferably less than 25 μA/cm², and is maintained atleast greater than 1 day of exposure, or preferably greater than 1 weekof exposure, and more preferably greater than 3 months of exposure.

It is appreciated that the above environmental stability ranges aremeasured with respect to cyclic voltammetry applied and measured between3 to 3V with a pair of blocking electrodes such as stainless steel,nickel, or aluminum.

The effect of the power density drawn from the printed microbattery onits discharge time was calculated and plotted in FIG. 22. As has beenreported for other electrochemical systems, when plotted on logarithmicaxes, the discharge time decreases linearly with greater applied powerdensity. With a 15 mW/cm² pulse, the battery fully discharged inapproximately 150 seconds. A maximum energy density of 1.49 mW/cm² isachieved for moderate power densities between 0.05-1 mW/cm², and beyondthis window, the energy density diminishes. From this plot a maximumpower density can be approximated as the value at which only 75% of thebattery's energy density is drawn; the maximum power density is 2mW/cm².

For applications in which the recharge of the battery occursinfrequently or with unknown intermittency, the battery's self-dischargebehavior (also known as leakage) is a critical property to investigate.By definition self-discharge in a battery is the progressive timedependent loss of charge typically due to coupled faradaic processesoccurring at the anode and cathode.

The rates and mechanisms of self-discharge in a battery can vary greatlywith cell potential. To determine the mechanism of self-discharge, themost common method is to monitor a cell's potential decay afterpolarizing it for a short time. For this experiment, there is noexternal circuit for charge to pass; therefore the rate of decreasingstate of charge must primarily depend on the self-discharge processeswithin the cell. The potential decay behavior can be used to distinguishbetween three types of self-discharge mechanisms: (1) self-discharge dueto coupled faradaic processes at the anode and cathode (2) diffusioncontrolled self discharge of electroactive impurities, or (3) shortcircuit leakage between the electrodes. For the first process whereself-discharge is attributable to faradaic reactions, for example due tothe continued solution decomposition in a cell after being overcharged,the leakage current (self-discharge) measured at a cell potential (V)can be approximated.

The potential decay of the battery after being exposed to charge pulses(with a positive current) is recorded in FIG. 23. The initial cellpotential (V_(initiai)) at t=0 s corresponds to the potential the cellwas polarized to during the charge pulse, and the cell is shown to relaxand equilibrate to a lower potential after 5 hours or 18,000 seconds.Over sixty charge pulses were applied to the battery leading to agradual increase in cell potential from 1.5 to 2.2 V. The plots of thecell's potential decay showed a gradual trend marching upwards due tothe increased addition of charge to the system. To determine themechanism of self-discharge, the cell potential was plotted in FIG. 24and FIG. 25 with respect to the logarithm and square root of time,corresponding to faradaic and diffusion controlled leakage mechanisms,respectively. Comparing the two figures, the self-discharge in theprinted battery is of faradaic origin due to coupled reactions at theanode and cathode rather than due to the diffusion of redox activeimpurities.

In FIG. 26, the slopes of these linear sweeps (dE/d[log(t)]) weregraphed with respect to the initial cell potential the battery waspolarized to; the negative slopes correspond to the rate of potentialdecay in the battery, and a trend of increased self-discharge rate (orgreater magnitude of dE/d[log(t)]) with higher polarization cellpotential is apparent. The contrast in rates of self-discharge for cellpotentials between 1.5 to 2.2 V indicates that the relative parasiticredox reactions occurring at the anode and cathode vary substantiallywith the cell's state of charge. Studies utilizing a reference electrodemay elucidate the magnitudes of leakage contributions and mechanisms ofself-discharge at each electrode. By subjecting the cell to a dischargepulse of opposite polarity but of the same magnitude and length of timeas the potential decay study above, the battery demonstrated interesting“recovery” behavior. What was observed in FIG. 27 was a gradual increasein the cell's potential when it was allowed to rest at open circuitafter a discharge pulse. As was applied in the self-discharge study, therelationship between cell potential and time was used to distinguish themechanism of self-recovery.

By plotting the cell potential data as a function of the logarithm FIG.28 and the square root of time FIG. 29, the linear behavior visible inFIG. 29 suggests that the recovery mechanism is not diffusioncontrolled, but rather dependent on the faradaic reactions of species atthe anode and cathode; the mechanism of self-recovery is consistent withthe self-discharge study. This observation is contrary to popularhypotheses on the recovery effect of batteries, which is typicallyattributed to the diffusion of electroactive ions in the electrolytetowards the electrodes to compensate for the large concentrationgradients formed during rapid polarization of the battery.

A complementary study to determine the voltage dependence of the leakagebehavior in an electrochemical system is the float current technique.The float current is the current needed to maintain the electrodes at acell potential. The float current exactly matches the magnitude of thespontaneous self-discharge current flowing in the cell and thereforeprevents the parasitic currents from diminishing the cell's state ofcharge. To determine the voltage dependence of the printed battery'sleakage, the cell's potential was held for eight hours and its currentresponse was measured. At the onset of holding the cell at a certainvoltage, the resulting current response exhibits its maximum value andthen gradually decays over time until it reaches steady state.

An example of the current measured in a printed battery held at 1.65 Vis shown in FIG. 30. The float current is estimated as the currentmeasured after eight hours of holding the cell at a given potential, andassumed to be equal in magnitude to the leakage currents occurringspontaneously in the cell. The amount of charge passed due to theseparasitic mechanisms is determined by integrating the area under thecurrent response curves, and from this a leakage power can becalculated. For the printed battery, the study was conducted over twosubsequently measured charge and discharge cycles. The charge cyclefloat currents recorded for cell potentials between 1.1 and 2 V showedan increasing trend with increasing state of charge. Both first andsecond charge cycles exhibited very similar leakage current quantitiesas well as increasing trends with escalating applied cell potential. Aconsiderable spike in float current between 1.62 and 1.84 V was detectedin both cycles, possibly indicating a repeatable leakage mechanismdependent on the state of charge (such as the electrochemical breakdownof an electrolyte constituent).

From the current measurements of the printed batteries, the chargepassed potentiostatically (FIGS. 31 and 32) was also plotted. The trendsfor the measured charge and power passed during the charge and dischargecycles matched that of the float current with cell potential, and ingeneral the measured properties of the first and second cycle exhibitedsimilar values. The leakage power upon charge varied between 0 to 6.4μW/cm², while upon discharge, the maximum leakage power measured was 2.5μW/cm². The average leakage power measured in the printed battery was1.38 μW/cm².

A study of the moisture tolerances of various electronics devices wasalso conducted. Devices which have minimal to moderate moisturetolerances can be packaged with as little as a single layer barrier suchas polyimide, silicone, glass, or a metal oxide film. For devicesincorporating organic materials that are environmentally sensitive suchas organic light emitting diodes (OLEDs) and organic transistors, themoisture tolerances, measured by the water vapor transmission rate(WVTR), of these devices are very low (<10⁻³ g/m²/day). These devicesrequire much more sophisticated barriers such as multilayer structuresalternating with organic and inorganic materials. According to a simpleestimation, a lithium battery can tolerate a WVTR no greater than 10⁻⁴.The estimation stems from the following relationship: WVTR is equal tothe thickness of sensitive component in battery, multiplied by itsdensity, and divided by desired lifetime. For a lithium battery where a3.5 μm thick lithium electrode is the most environmentally sensitivecomponent and the battery must last 10 years, an assumption of a 1:1mass reactant ratio results in an WVTR estimation of 5*10⁻⁴ g/m²/day.The WVTR of a lithium battery is equal to 5×10⁻⁴ g/m²/day. If this wereadjusted to account for a 1:1 mole reaction ratio, this reduces the WVTRfurther below 1*10⁻⁵ g/m²/day for the same battery and lifetimerequirement.

Various current collector material were also tested for compatibilityand stability with the gel electrolyte of the present invention.

FIG. 33 shows voltammograms of symmetric cells containing two adjacentlyprinted or patterned copper, silver, nickel and aluminum currentcollector films, each covered in the printed gel electrolyte 12 of thepresent invention. The electrochemical stabilities/instabilities ofcopper, silver, nickel and aluminum in the gel electrolyte correspondwith the magnitude of current density detected for a given potential.

As shown in FIG. 33, the copper and silver current collectors were shownto be electrochemically unstable, demonstrating a leakage current in theionic liquid electrolyte >50 μA/cm² at potentials greater than 0.5V andless than −0.5V.

Using a planar test cell, an ink composed of 93 wt. % spherical nickelpowder [E-Fill, Sulzer Metco Canada] and 7 wt. % PVDF-HFP was subjectedto a 10 mV/s CV scan rate between −2 to 2 V. The nickel exhibited fairlystable behavior with the gel electrolyte, with negligible currentdensities and no morphology changes detected at the current collectorinterfaces over 25 cycles.

Aluminum current collectors having thickness between 1 μm and 80 μm andmaterial composition of aluminum foil, aluminum nanoparticles, oraluminum composites where aluminum powder is mixed with a polymer binderwas deposited or adhered to a plastic or glass substrate. It isappreciated that the aluminum current collector may also be deposited orpatterned using die cutting, screen printing, dispenser printing, inkjet printing, or cold-foil or hot-foil printing methods. As shown inFIG. 33 an aluminum foil current collector also showed stability acrossthe range of range of −3 to 3 V.

FIG. 34 shows voltammograms showing stability at various temperatures ofwhich the aluminum foil current collectors and gel electrolyte wereexposed to. Stability was shown for temperatures ranging from 25° C. to125° C.

3. Printed Capacitor

An electrochemical capacitor was fabricated using the printing methodillustrated in FIGS. 35A through 35C. At step 122 shown in FIG. 35A, afirst carbon electrode layer 132 is printed directly onto the substrate68. Carbon electrode layer 132 is printed onto the substrate 68 as afirst ink dispenser 140 passes over the substrate 68. At step 124 shownin FIG. 35B, a gel electrolyte layer 134 is printed directly onto thefirst carbon electrode layer 132 as a second ink dispenser 142 passesover the first carbon electrode layer 132. At step 126 shown in FIG.35C, a second carbon electrode layer 136 is printed directly onto thegel electrolyte layer 134 as a third ink dispenser 144 passes over thegel electrolyte layer 134.

FIG. 36 shows a micrograph of a printed capacitor 130 cross sectionprinted according to the method of FIGS. 35A-C. The cross section showsa first carbon electrode 132 spaced apart from a second carbon electrodeby a gel electrolyte 134.

The carbon electrochemical capacitor electrode inks of the capacitor 130shown in FIG. 36 comprised composite slurries composed of 50 wt. %activated high surface area carbon powder, 2 wt. % conductive carbonadditives, 24 wt. % conductive carbon additives, 24 wt. % polyvinylidenefluoride (PVDF) polymer binder, and 24 wt. % tetrafluoroborate(BMIM+BF₄−) ionic liquid electrolyte. The slurry's rheology was tailoredusing N-methylpyrrolidone (NMP) solvent, which later evaporates upondrying. The capacitor's gel electrolyte 134 is composed of equal partsPVDF and the BMIM⁺BF₄ ⁻. Commercial foils of stainless steel and nickelwere used as current collector films. All inks are mixed untilhomogenous, and then deposited sequentially in the configuration shownin FIGS. 35A-C. Between film deposition steps the films were dried at70° C. for 20 minutes. The typical substrate used for these testsstructures was glass.

It should be noted that the gel electrolyte 134 of the capacitor 130 ofFIG. 36 used a significantly different composition than the electrolyticgel 12 of the battery 10 illustrated in FIG. 1. While not tested, it isappreciated that an electrolytic gel similar to the battery 10illustrated in FIG. 1 may also be incorporated for use with thecapacitor 130.

Cyclic voltammetry and electrochemical impedance spectroscopyexperiments were conducted with a Gamry Reference 600Potentiostat/Galvanostat/ZRA. All .AC impedance measurements were takenpotentiostatically with a DC voltage of 0V and an AC voltage of 5 mVwithin a frequency range of 10 mHz-10 kHz. Measurements are normalizedusing the capacitor footprint area (not the surface area of theelectrode) as this area usually is the most restrictive parameter indesigning micro-energy storage for small devices.

FIG. 37 shows the cycle life vs. capacitance of the printedelectrochemical capacitor 130. FIG. 38 is a plot of the charge anddischarge cycle of the printed electrochemical capacitor. FIG. 39illustrates the pulsed behavior of the printed capacitor 130 at 1 mA,and 0.1 mA.

4. Cell Applications

FIG. 40 illustrates an example of an active RFID tag 150 utilizing theenergy storage component 152, thermal or solar energy harvestingcomponent 154, and sensor 156 (e.g. MEMS cantilever sensor). The energystorage component 152 may comprise a printed microbattery, such as cell10 in FIG. 1, which is printed directly to the circuit board using“printing on green” method described below with respect to FIG. 39.

For applications operating over long device lifetimes (>10 years withoutthe ability to replace its power source if depleted), the incorporationof an energy harvesting device 154 to convert ambient energy to usefulelectrical energy is paramount. Obstacles to the incorporation of energyharvesting technologies in current devices include its high cost andintermittency of power supplied. The printed microbatteries 10 of thepresent invention add inherent value to energy harvesting devicesbecause of its simple integration procedure that enables versatile formfactors and customizable performance properties. As most energyharvesters are materials, processing, and energy intensive to fabricate,pairing these devices with a low-cost energy storage device that iseasily integrated with minimal materials, waste, and energy inputs addssignificant utility. More importantly, energy storage bridgesdiscrepancies in power demands with the power supplied by the harvester.

In most applications and environments, the combination of energyharvester 154 and storage device 152, known as a hybrid power supply,are highly desirable. Alone, electrochemical capacitors (e.g. capacitor130 of FIG. 36) are limited in energy density compared to batteries, butare appropriate for scenarios requiring frequent, high power pulseoperation such as in emergency response applications, which rely onrapid real-time information. Electrochemical capacitors 130 are alsocomplementary technology when used with batteries (e.g. battery 10) forapplications requiring larger energy storage capacity, and if used inconjunction, the capacitor can address high power surges demanded fromthe load, effectively mitigating detrimental battery operation andtherefore increasing the battery's and consequently the device'slifetimes.

Dispenser printing methods may be used to integrate an energy storagedevice on the substrate area surrounding MEMS vibration energyharvesters that are microfabricated onto a silicon die. The dispenserprinter also offers the added benefit of being able to tailor the energystorage performance properties to be compatible with the power suppliedby the energy harvester 154 as well as the power demanded by the load,which both can vary significantly with the environment it is calibratedin.

On a crowded printed circuit board (PCB) with limited unoccupiedsubstrate area, the printing methods of the present invention have theability to fill any open space with an energy storage component(s),effectively depositing the maximum amount of energy storage within acrowded substrate. This concept, also known as “printing on green,” isillustrated in the method 170 shown in FIG. 41.

At step 172, a printed circuit board 184 is provided having variouscomponents 182. At step 174 empty space 186 is determined for printingenergy storage. At step 176, a device print design 188 is generatedbased on the available footprint in the PCB 184. At step 178, energystorage device 190 is printed on the board 184 to generate theintegrated device shown in step 180. Note that this process is carriedout in ambient conditions and minimal post processing temperatures(<150° C.), therefore it avoids damaging any neighboring components thatmight be sensitive to environmental exposure.

Along with being able to print in inaccessible areas on a crowdedsubstrate, the dispenser printer is also capable of printing conformablyon non-planar surfaces (e.g. a curved surface). This adds greaterflexibility in where energy storage devices can be integrated on adevice. On a crowded substrate, an electrically insulating layer can beprinted on top of any components, and then conformably coated with aprinted microbattery. Since all fabrication and post-processing of themicrobattery occurs at ambient conditions and temperatures under 120°C., all neighboring components should not be damaged in the process.

The capability of depositing custom microbatteries both in the openspace as well as conformably on device components provides extensivepossibilities for the on-demand fabrication of localized energy storagecomponents. Traditionally, an electronic device obtains its power from asingle source, such as a primary battery. If any of its componentsrequire different supply voltages, additional power circuitry is neededto convert the battery voltage to its required value. The efficiency ofa voltage conversion operation will vary with the type of conversionmethod used: linear regulators are simple and low-cost, but are veryinefficient for large voltage changes, resulting in unwanted heatdissipation. Switched-mode voltage converters (such as switchedcapacitors) can be designed to be very efficient (>75%) and by usingCMOS fabrication, the devices are less area intensive compared to linearregulators, however they are complex to design and integrate. In thisdiscussion it is assumed that a typical wireless sensor contains amicrocontroller typically comprised of an oscillator and control unit, acommunication component(s) such as a transceiver and/or receiver, asensor(s), and a power supply.

The use of micro energy storage devices as local supply voltages andpower sources can mitigate the design complexities and conversioninefficiencies associated with power regulation as well as reduce thesubstrate area dedicated power circuitry. Added functionality and arealfootprint efficiency is achieved by fabricating stacked series andparallel configurations of microbatteries and capacitors. This should beachievable using dispenser printing, but has yet to be fullydemonstrated. Localized energy storage components can be tailoredaccording to their use; rather than pulsing a battery with acumulatively high power draw derived from the sum of many components, ahighly tailored energy storage device can be dedicated to eachindividual component.

For example, a microcontroller unit typically draws a continual lowpower (<10 μW) and may be suitably powered by a local microbattery ofthe chemistry provided herein. On the other hand, a transceiver requiresinfrequent high bursts of power. This behavior may be better addressedby an electrochemical capacitor (e.g. capacitor 130) or batterychemistry capable of handling high rates of discharge (such aszinc-silver oxide). By exploiting their advantages and separating theenergy storage components, the overall cumulative health of the energystorage network may exceed that of traditional single battery poweredsystem. To encourage this design paradigm change, simulations anddemonstrations of this concept are needed.

Along with the applications discussed, flexible electronics provides aunique opportunity for printed microbatteries. Relevant markets includelow-cost active RFID tags for asset management and printed media. Byutilizing polymer-based materials microbatteries 10 of the presentinvention can be reasonably bent and conformed to non-planar substrateswithout damage. Furthermore, most flexible substrates are polymermaterials which cannot be processed beyond 150-200° C. The printingmethod of the present invention enables near room temperature depositionand post processing, and are compatible with these substrates.

From the discussion above it will be appreciated that the invention canbe embodied in various ways, including the following:

1. An electrochemical cell, comprising an anode layer; a cathode layer;and a non-aqueous gel electrolyte layer coupled to the anode layer andcathode layer; said electrolyte layer providing physical separationbetween the anode layer and the cathode layer; said gel electrolytelayer comprising a polymer into which at least one ionic liquid and anelectrolyte salt have been imbibed; said electrolyte layer comprising acomposition configured to provide ionic communication between the anodelayer and cathode layer by facilitating transmission of multivalent ionsbetween the anode layer and the cathode layer.

2. An electrochemical cell as recited in embodiment 1, wherein the anodelayer, cathode layer, and electrolyte layer comprise flexible,compressible layers capable of deformation without significant loss ofperformance.

3. An electrochemical cell as recited in embodiment 2, wherein the cellcomprises a battery cell.

4. An electrochemical cell as recited in embodiment 3, wherein thebattery cell is a rechargeable battery cell.

5. An electrochemical cell as recited in embodiment 1, furthercomprising: a first current collector in electronic communication withthe cathode; and a second current collector in electronic communicationwith the anode.

6. An electrochemical cell as recited in embodiment 1, wherein one ormore of the anode layer, cathode layer, electrolyte layer and currentcollectors are configured to be deposited an a substrate in a liquidform, and solidify to at least a semi-solid state after a period oftime.

7. An electrochemical cell as recited in embodiment 1, wherein the cellis configured to operate in an ambient environment for over 4 monthswith no additional packaging.

8. An electrochemical cell as recited in embodiment 1, wherein thepolymer network comprises one or more polymer(s) selected from the groupconsisting of poly(vinylidene fluoride) (PVDF), poly(vinylidenefluoride-hexafluoropropylene) (PVDF-HFP), polyvinyl alcohol (PVA),poly(ethylene oxide) (PEO), poly(acrylo-nitrile) (PAN), and poly(methylmethacrylate) (PMMA), epoxy derivatives, and silicone derivatives.

9. An electrochemical cell as recited in embodiment 1, wherein theelectrolyte salt dissolved into the ionic liquid releases cationsselected from the group consisting of zinc ions (Zn²⁺), aluminum (Al³⁺),magnesium (Mg²⁺), and yttrium (Y²⁺).

10. An electrochemical cell as recited in embodiment 1, wherein the saltdissolved into the ionic liquid releases anions selected from the groupconsisting of chlorides, tetrafluoroborate (BF4−), trifluoroacetate(CF3CO2−), trifluoromethansulfonate (CF3SO3−), hexafluorophosphate(PF6−), bis(trifluoromethylsulfonyl)amide (NTf2−), andbis(fluorosulfonyl)imide (N(SO2F)2−).

11. An electrochemical cell as recited in embodiment 1, wherein theionic liquid is a room temperature salt having cations selected from thegroup consisting of imidazolium variants, pyrrolidinium variants,ammonium variants, pyridinium variants, piperidinium variants,phosphonium variants, and sulfonium variants.

12. An electrochemical cell as recited in embodiment 11, wherein theionic liquid is a room temperature salt having anions selected from thegroup consisting of chlorides, tetrafluoroborate (BF4−),trifluoroacetate (CF3CO2−), trifluoromethansulfonate (CF3SO3−),hexafluorophosphate (PF6−), bis(trifluoromethylsulfonyl)amide (NTf2−),and bis(fluorosulfonyl)imide (N(SO2F)2−).

13. An electrochemical cell as recited in embodiment 1, wherein theanode comprises a component selected from the group consisting of zinc,aluminum, magnesium, and yttrium.

14. An electrochemical cell as recited in embodiment 1, wherein thecathode comprises a metal oxide.

15. An electrochemical cell as recited in embodiment 14, wherein metaloxide comprises a component selected from one or more of the groupconsisting of vanadium pentoxide (V₂O₅), manganese dioxide (MnO₂),cobalt oxide (Co_(x)O_(y)), titanium oxide (Ti_(x)O_(y)), and lead oxide(Pb_(x)O_(y)).

16. An electrochemical cell as recited in embodiment 5, wherein thecurrent collectors comprise a metal foil comprising a metal selectedfrom the group consisting of nickel, stainless steel, gold, andaluminum.

17. An electrochemical cell as recited in embodiment 1, wherein theanode layer and the cathode layer each have thicknesses between 8 μm and60 μm.

18. An electrochemical cell as recited in embodiment 1, wherein theelectrolyte has a thickness between approximately 1 μm and 15 μm.

19. An electrochemical cell as recited in embodiment 5, wherein thecurrent collectors comprise printed layers each having thicknessesbetween 8 μm and 60 μm.

20. An electrochemical cell as recited in embodiment 5, wherein thecurrent collectors comprise metallic foils each having thicknessesbetween 1 μm and 80 μm.

21. An electrochemical cell as recited in embodiment 1, wherein theliquid electrolyte comprises a zinc salt concentration between 0.2 and0.75 M in ionic liquid.

22. An electrochemical cell as recited in embodiment 21, wherein theliquid electrolyte comprises a zinc salt concentration between 0.4 and0.75 M.

23. An electrochemical cell as recited in embodiment 21, wherein theliquid electrolyte comprises a zinc salt concentration between 0.45 and0.65 M.

24. An electrochemical cell as recited in embodiment 22, wherein theliquid electrolyte has an ionic conductivity above 2.3 mS/cm.

25. An electrochemical cell as recited in embodiment 1, wherein theelectrochemical cell has a current density output ranging between 0.001mA/cm² and 100 mA/cm².

26. An electrochemical cell as recited in embodiment 1, wherein the gelelectrolyte layer is configured to maintain an output leakage currentdensity of less than 50 μA/cm² while being exposed to temperaturesranging from 20° C. and 45° C. for a period greater than 3 months.

27. An electrochemical cell as recited in embodiment 26, wherein the gelelectrolyte layer is configured to maintain an output leakage currentdensity of less than 25 μA/cm² while being exposed to temperaturesranging from 20° C. and 45° C. for a period greater than 3 months.

28. An electrochemical cell as recited in embodiment 27, wherein the gelelectrolyte layer is configured to maintain an output leakage currentdensity of less than 15 μA/cm² while being exposed to temperaturesranging from 20° C. and 45° C. for a period greater than 3 months.

29. An electrochemical cell as recited in embodiment 1, wherein the gelelectrolyte layer is configured to maintain an output leakage currentdensity of less than 75 μA/cm² while being exposed to temperaturesranging from 45° C. and 90° C. for a period greater than 1 month.

30. An electrochemical cell as recited in embodiment 29, wherein the gelelectrolyte layer is configured to maintain an output leakage currentdensity of less than 50 μA/cm² while being exposed to temperaturesranging from 45° C. and 90° C. for a period greater than 1 month.

31. An electrochemical cell as recited in embodiment 30, wherein the gelelectrolyte layer is configured to maintain an output leakage currentdensity of less than 40 μA/cm² while being exposed to temperaturesranging from 45° C. and 90° C. for a period greater than 1 month.

32. An electrochemical cell as recited in embodiment 1, wherein the gelelectrolyte layer is configured to maintain an output leakage currentdensity of less than 15 μA/cm² while being exposed to ambientenvironment for a period greater than 6 months.

33. An electrochemical cell as recited in embodiment 1, wherein the gelelectrolyte layer is configured to maintain an output leakage currentdensity of less than 50 μA/cm² while being exposed to temperaturesranging from −20° C. and 20° C. for a period greater than 3 months.

34. An electrochemical cell as recited in embodiment 33, wherein the gelelectrolyte layer is configured to maintain an output leakage currentdensity of less than 25 μA/cm² while being exposed to temperaturesranging from −20° C. and 20° C. for a period greater than 3 months.

35. An electrochemical cell as recited in embodiment 34, wherein the gelelectrolyte layer is configured to maintain an output leakage currentdensity of less than 15 μA/cm² while being exposed to temperaturesranging from −20° C. and 20° C. for a period greater than 3 months.

36. An electrochemical cell as recited in embodiment 1, wherein the gelelectrolyte layer is configured to maintain an output leakage currentdensity of less than 75 μA/cm² while being exposed to temperatures lessthan −20° C. for a period greater than 1 day.

37. An electrolyte configured to provide physical separation between ananode and the cathode of an electromechanical cell, comprising: a roomtemperature ionic liquid electrolyte and dissolved salt imbibed into apolymer to form a non-aqueous gel; the electrolyte comprising acomposition configured to provide ionic communication between the anodeand cathode by facilitating transmission of multivalent ions across theelectrolyte.

38. An electrolyte as recited in embodiment 37, wherein the electrolytecomprises a polymer into which at least one ionic liquid and anelectrolyte salt have been imbibed.

39. An electrolyte as recited in embodiment 37, wherein the polymercomprises one or more polymer(s) selected from the group consisting ofpoly(vinylidene fluoride) (PVDF), poly(vinylidenefluoride-hexafluoropropylene) (PVDF-HFP), polyvinyl alcohol (PVA),poly(ethylene oxide) (PEO), poly(acrylo-nitrile) (PAN), and poly(methylmethacrylate) (PMMA), epoxy derivatives, and silicone derivatives.

40. An electrolyte as recited in embodiment 38, wherein the ionic liquidis a room temperature salt having cations selected from the groupconsisting of imidazolium variants, pyrrolidinium variants, ammoniumvariants, pyridinium variants, piperidinium variants, phosphoniumvariants, and sulfonium variants.

41. An electrolyte as recited in embodiment 40, wherein the ionic liquidis a room temperature salt having anions selected from the groupconsisting of chlorides, tetrafluoroborate (BF4−), trifluoroacetate(CF3CO2−), trifluoromethansulfonate (CF3SO3−), hexafluorophosphate(PF6−), bis(trifluoromethylsulfonyl)amide (NTf2−), andbis(fluorosulfonyl)imide (N(SO2F)2−).

42. An electrolyte as recited in embodiment 1, wherein the electrolyteis configured to be disposed in a gel layer having a thickness down toapproximately 1 μm.

43. An electrolyte as recited in embodiment 42, wherein the liquidelectrolyte comprises a zinc salt concentration between 0.2 and 0.75 Min ionic liquid.

44. An electrolyte as recited in embodiment 43, wherein the liquidelectrolyte comprises a zinc salt concentration between 0.4 and 0.75 M.

45. An electrolyte as recited in embodiment 44, wherein the liquidelectrolyte comprises a zinc salt concentration between 0.45 and 0.65 M.

46. An electrolyte as recited in embodiment 44, wherein the liquidelectrolyte has an ionic conductivity above 2.3 mS/cm.

47. An electrolyte as recited in embodiment 42, wherein the gelelectrolyte layer is configured to maintain an output leakage currentdensity of less than 50 μA/cm² while being exposed to temperaturesranging from 20° C. and 45° C. for a period greater than 3 months.

48. An electrolyte as recited in embodiment 47, wherein the gelelectrolyte layer is configured to maintain an output leakage currentdensity of less than 25 μA/cm² while being exposed to temperaturesranging from 20° C. and 45° C. for a period greater than 3 months.

49. An electrolyte as recited in embodiment 48, wherein the gelelectrolyte layer is configured to maintain an output leakage currentdensity of less than 15 μA/cm² while being exposed to temperaturesranging from 20° C. and 45° C. for a period greater than 3 months.

50. An electrolyte as recited in embodiment 42, wherein the gelelectrolyte layer is configured to maintain an output leakage currentdensity of less than 75 μA/cm² while being exposed to temperaturesranging from 45° C. and 90° C. for a period greater than 1 month.

51. An electrolyte as recited in embodiment 50, wherein the gelelectrolyte layer is configured to maintain an output leakage currentdensity of less than 50 μA/cm² while being exposed to temperaturesranging from 45° C. and 90° C. for a period greater than 1 month.

52. An electrolyte as recited in embodiment 51, wherein the gelelectrolyte layer is configured to maintain an output leakage currentdensity of less than 40 μA/cm² while being exposed to temperaturesranging from 45° C. and 90° C. for a period greater than 1 month.

53. An electrolyte as recited in embodiment 42, wherein the gelelectrolyte layer is configured to maintain an output leakage currentdensity of less than 15 μA/cm² while being exposed to ambientenvironment for a period greater than 6 months.

54. An electrolyte as recited in embodiment 42, wherein the gelelectrolyte layer is configured to maintain an output leakage currentdensity of less than 50 μA/cm² while being exposed to temperaturesranging from −20° C. and 20° C. for a period greater than 3 months.

55. An electrolyte as recited in embodiment 54, wherein the gelelectrolyte layer is configured to maintain an output leakage currentdensity of less than 25 μA/cm² while being exposed to temperaturesranging from −20° C. and 20° C. for a period greater than 3 months.

56. An electrolyte as recited in embodiment 55, wherein the gelelectrolyte layer is configured to maintain an output leakage currentdensity of less than 15 μA/cm² while being exposed to temperaturesranging from −20° C. and 20° C. for a period greater than 3 months.

57. An electrolyte as recited in embodiment 42, wherein the gelelectrolyte layer is configured to maintain an output leakage currentdensity of less than 75 μA/cm² while being exposed to temperatures lessthan −20° C. for a period greater than 1 day.

58. A method of fabricating an electrochemical cell, comprising thesteps of: providing a first electrode ink and a second electrode ink;providing liquid electrolyte ink; printing a first electrode layer ofthe first electrode ink; printing a layer of electrolyte ink; andprinting a second electrode layer of second electrode ink; wherein thelayer of electrolyte ink that provides physical separation between thefirst electrode layer and second electrode layer to form anelectrochemical cell; and wherein the electrolyte layer is configured toprovide ionic communication between the first electrode layer and secondlayer by facilitating transmission of multivalent ions between the firstelectrode layer and the second electrode layer.

59. A method as recited in embodiment 58, further comprising: providinga current collector ink; and printing a layer of current collector inkadjacent to one or more of the first electrode layer and the secondelectrode layer.

60. A method as recited in embodiment 58, wherein the electrochemicalcell is fabricated at ambient temperature.

61. A method as recited in embodiment 60, wherein the electrochemicalcell is fabricated at ambient pressure.

62. A method as recited in embodiment 58, wherein the inks are liquidsselected from the group consisting of solutions, suspensions, andslurries.

63. A method as recited in embodiment 58, wherein the first and secondelectrode inks comprise slurries of active electrode particles, polymerbinder, optional additives, and a solvent(s).

64. A method as recited in embodiment 58, wherein the electrolytecomprises a polymer into which at least one ionic liquid and at leastone electrolyte salt have been imbibed.

65. A method as recited in embodiment 64, wherein the polymer comprisesone or more polymer(s) selected from the group consisting ofpoly(vinylidene fluoride) (PVDF), poly(vinylidenefluoride-hexafluoropropylene) (PVDF-HFP), polyvinyl alcohol (PVA),poly(ethylene oxide) (PEO), poly(acrylo-nitrile) (PAN), and poly(methylmethacrylate) (PMMA), epoxy derivatives, and silicone derivatives.

66. A method as recited in embodiment 64, wherein the ionic liquid is aroom temperature salt having cations selected from the group consistingof imidazolium variants, pyrrolidinium variants, ammonium variants,pyridinium variants, piperidinium variants, phosphonium variants, andsulfonium variants.

67. A method recited in embodiment 66, wherein the ionic liquid is aroom temperature salt having anions selected from the group consistingof chlorides, tetrafluoroborate (BF4−), trifluoroacetate (CF3CO2−),trifluoromethansulfonate (CF3SO3−), hexafluorophosphate (PF6−),bis(trifluoromethylsulfonyl)amide (NTf2−), and bis(fluorosulfonyl)imide(N(SO2F)2−).

68. A method as recited in embodiment 64, wherein the first electrodelayer comprises a component selected from the group consisting of zinc,aluminum, magnesium, and yttrium.

69. A method as recited in embodiment 64, wherein the second electrodelayer comprises particles selected from the group consisting of a metaloxide.

70. A method as recited in embodiment 58, wherein at least one of saidprinting steps is done using a direct write dispenser method.

71. A method as recited in embodiment 58, wherein at least one of saidprinting steps is done using a method selected from the followingmethods: screen-printing, gravure printing, pad printing, ink jetprinting, flexographic coating, spray coating, ultrasonic spray coating,or slot die coating.

Although the description above contains many details, these should notbe construed as limiting the scope of the invention but as merelyproviding illustrations of some of the presently preferred embodimentsof this invention. Therefore, it will be appreciated that the scope ofthe present invention fully encompasses other embodiments which maybecome obvious to those skilled in the art, and that the scope of thepresent invention is accordingly to be limited by nothing other than theappended claims, in which reference to an element in the singular is notintended to mean “one and only one” unless explicitly so stated, butrather “one or more.” All structural, chemical, and functionalequivalents to the elements of the above-described preferred embodimentthat are known to those of ordinary skill in the art are expresslyincorporated herein by reference and are intended to be encompassed bythe present claims. Moreover, it is not necessary for a device or methodto address each and every problem sought to be solved by the presentinvention, for it to be encompassed by the present claims. Furthermore,no element, component, or method step in the present disclosure isintended to be dedicated to the public regardless of whether theelement, component, or method step is explicitly recited in the claims.No claim element herein is to be construed under the provisions of 35U.S.C. 112, sixth paragraph, unless the element is expressly recitedusing the phrase “means for.”

What is claimed is:
 1. An electrochemical cell, comprising: an anode; acathode; and a printed gel electrolyte between the anode and thecathode, wherein the electrolyte is configured to provide ioniccommunication between the anode and the cathode to facilitatetransmission of multivalent ions between the anode and the cathode,wherein the multivalent ions are selected from at least one of zinc,aluminum, magnesium and yttrium, and wherein the electrochemical celldisplays substantially no capacity degradation after at least 70 cycles.2. The electrochemical cell of claim 1, wherein the gel electrolytecomprises a polymer into which an ionic liquid and an electrolyte saltare imbibed.
 3. The electrochemical cell of claim 2, wherein the ionicliquid comprises cations selected from the group consisting of:imidazolium, pyrrolidinium, ammonium, pyridinium, piperidinium,phosphonium, and sulfonium.
 4. The electrochemical cell of claim 2,wherein the ionic liquid comprises anions selected from the groupconsisting of: chlorides, tetrafluoroborate (BF₄−), trifluoroacetate(CF₃CO₂−), trifluoromethansulfonate (CF₃SO₃−), hexafluorophosphate(PF₆−), bis(trifluoromethylsulfonyl)amide (NTf₂−), andbis(fluorosulfonyl)imide (N(SO₂F)₂−).
 5. The electrochemical cell ofclaim 2, wherein the salt releases cations selected from the groupconsisting of zinc, aluminum, magnesium and yttrium.
 6. Theelectrochemical cell of claim 2, wherein the salt releases anionsselected from the group consisting of chlorides, tetrafluoroborate(BF4−), trifluoroacetate (CF₃CO₂−), trifluoromethansulfonate (CF₃SO₃−),hexafluorophosphate (PF₆−), bis(trifluoromethylsulfonyl)amide (NTf₂−),and bis(fluorosulfonyl)imide (N(SO₂F)₂−).
 7. The electrochemical cell ofclaim 2, wherein the polymer comprises at least one polymer selectedfrom the group consisting of poly(vinylidene fluoride) (PVDF),poly(vinylidene fluoride) hexaflourophosphate (PVDF-HFP), polyvinylalcohol (PVA), poly(ethylene oxide) (PEO), poly(acrylo-nitrile) (PAN),and poly(methyl methacrylate) (PMMA), epoxy derivatives, and siliconederivatives.
 8. The electrochemical cell of claim 2, wherein the gelelectrolyte comprises a weight percentage of the ionic liquid to thepolymer not exceeding 75 wt %.
 9. The electrochemical cell of claim 1,wherein the printed gel electrolyte has an ionic conductivity between0.3 mS/cm and 2.7 mS/cm.
 10. The electrochemical cell of claim 1,wherein the anode comprises at least one of zinc, aluminum, magnesiumand yttrium.
 11. The electrochemical cell of claim 10, wherein the anodecomprises zinc.
 12. The electrochemical cell of claim 1, wherein thecathode comprises a metal oxide.
 13. The electrochemical cell of claim12, wherein the metal oxide comprises a component selected from thegroup consisting of vanadium pentoxide (V₂O₅), manganese dioxide (MnO₂),cobalt oxide (Co_(x)O_(y)), titanium oxide (Ti_(x)O_(y)), and lead oxide(Pb_(x)O_(y)).
 14. The electrochemical cell of claim 13, wherein themetal oxide is manganese dioxide (MnO₂).
 15. The electrochemical cell ofclaim 1, wherein the gel electrolyte is configured to maintain a leakagecurrent density of less than 25 pA/cm² after being exposed to atemperature of 20° C. for a period of greater than 1 week.
 16. Theelectrochemical cell of claim 1, wherein the gel electrolyte isconfigured to maintain a leakage current density of less than 50 pA/cm²after being exposed to a temperature of between 20° C. and 45° C. for aperiod of greater than 1 day.
 17. The electrochemical cell of claim 1,wherein the electrochemical cell is configured to output a currentdensity of between 0.001 mA/cm² to 100 mA/cm².
 18. The electrochemicalcell of claim 1, wherein the gel electrolyte is a flexible electrolytegel.
 19. The electrochemical cell of claim 1, wherein theelectrochemical cell is not hermetically sealed.
 20. The electrochemicalcell of claim 1, wherein the electrochemical cell is configured to beconformable to a non-planar substrate without damage.